diff --git a/crates/doc/src/edit.rs b/crates/doc/src/edit.rs
index a1f21f975..ed6ace82e 100644
--- a/crates/doc/src/edit.rs
+++ b/crates/doc/src/edit.rs
@@ -193,85 +193,140 @@ impl Document {
         Ok((id, sid))
     }
 
-    /// Thread `from` → `to`: `to` joins `from`'s story right after `from`. If `to` held its own text,
-    /// that text is appended to the story (as a new paragraph) and its old story is removed.
+    /// Thread `from` → `to`: `to` joins `from`'s story right after `from` (between `from` and the
+    /// frame that followed it, if any). If `to` held its own text, that text is appended to the
+    /// story (as new paragraphs) and its old story is removed; frames that followed `to` come
+    /// along, frames before it keep an empty story of their own. An empty (unassigned) `from` or
+    /// `to` becomes a text frame. `from`'s story keeps its id.
     pub fn thread(&mut self, from: ItemId, to: ItemId) -> Result<()> {
         if from == to {
             return Err(DocError::Invalid("cannot thread a frame to itself".into()));
         }
-        let fs = self.item(from).and_then(|i| i.text_frame()).map(|t| t.story).ok_or(DocError::NoItem(from))?;
-        // Convert unassigned/graphic-less frames into text frames.
-        let ts = match self.item(to).ok_or(DocError::NoItem(to))?.content.clone() {
-            Content::Text(t) => Some(t.story),
-            Content::Unassigned => None,
-            _ => return Err(DocError::Invalid("can only thread to text or empty frames".into())),
+        let ts = self.frame_story(to)?;
+        let fs = match self.frame_story(from)? {
+            Some(s) => s,
+            None => self.give_empty_story(from)?,
         };
         if ts == Some(fs) {
             return Err(DocError::Invalid("frames are already in the same story".into()));
         }
-        if let Some(ts) = ts {
-            let other = self.stories.remove(&ts).ok_or(DocError::NoStory(ts))?;
-            let other = Arc::unwrap_or_clone(other);
-            // Frames of the other story after `to` follow along; frames before it are left as empty new stories.
-            let pos_to = other.frames.iter().position(|f| *f == to).unwrap_or(0);
-            let before: Vec<ItemId> = other.frames[..pos_to].to_vec();
-            let after: Vec<ItemId> = other.frames[pos_to..].to_vec();
-            {
-                let st = self.story_mut(fs).ok_or(DocError::NoStory(fs))?;
-                if !other.text.is_empty() {
-                    st.text.push('\n');
-                    st.text.push_str(&other.text);
-                    st.paras.extend(other.paras.iter().cloned());
-                    // Char runs: '\n' takes the last run's format, then the other story's runs.
-                    if let Some(last) = st.chars.last_mut() {
-                        last.len += 1;
-                    }
-                    st.chars.extend(other.chars.iter().filter(|r| r.len > 0).cloned());
-                    st.tables.extend(other.tables.iter().map(|(k, v)| (*k, v.clone())));
-                    for n in &other.notes {
-                        let id = st.next_note_id();
-                        st.notes.push(Arc::new(crate::Footnote { id, text: n.text.clone() }));
-                    }
-                    st.anchors.extend(other.anchors.iter().cloned());
-                    st.xrefs.extend(other.xrefs.iter().cloned());
-                    st.index_refs.extend(other.index_refs.iter().cloned());
-                    st.objects.extend(other.objects.iter().cloned());
-                    st.rev += 1;
-                }
-                let at = st.frames.iter().position(|f| *f == from).map_or(st.frames.len(), |p| p + 1);
-                for (k, f) in after.iter().enumerate() {
-                    st.frames.insert(at + k, *f);
-                }
-            }
-            for f in &after {
-                if let Some(t) = self.item_mut(*f).and_then(Item::text_frame_mut) {
-                    t.story = fs;
-                }
-            }
-            if !before.is_empty() {
-                let nid = StoryId(self.alloc());
-                let mut ns = Story::new(nid);
-                ns.frames = before.clone();
-                for f in &before {
-                    if let Some(t) = self.item_mut(*f).and_then(Item::text_frame_mut) {
-                        t.story = nid;
-                    }
-                }
-                self.stories.insert(nid, Arc::new(ns));
-            }
-        } else {
+        let Some(ts) = ts else {
             let st = self.story_mut(fs).ok_or(DocError::NoStory(fs))?;
             let at = st.frames.iter().position(|f| *f == from).map_or(st.frames.len(), |p| p + 1);
             st.frames.insert(at, to);
+            st.rev += 1;
             let it = self.item_mut(to).ok_or(DocError::NoItem(to))?;
             it.content = Content::Text(TextFrame { story: fs, options: TextFrameOptions::default() });
-        }
-        if let Some(st) = self.story_mut(fs) {
+            return Ok(());
+        };
+        let mut other = Arc::unwrap_or_clone(self.stories.remove(&ts).ok_or(DocError::NoStory(ts))?);
+        // Frames of the other story from `to` on follow along; frames before it are left as an empty new story.
+        let pos_to = other.frames.iter().position(|f| *f == to).unwrap_or(0);
+        let after = other.frames.split_off(pos_to);
+        let before = std::mem::take(&mut other.frames);
+        {
+            let st = self.story_mut(fs).ok_or(DocError::NoStory(fs))?;
+            st.append_story(other);
+            let at = st.frames.iter().position(|f| *f == from).map_or(st.frames.len(), |p| p + 1);
+            for (k, f) in after.iter().enumerate() {
+                st.frames.insert(at + k, *f);
+            }
             st.rev += 1;
         }
+        for f in &after {
+            if let Some(t) = self.item_mut(*f).and_then(Item::text_frame_mut) {
+                t.story = fs;
+            }
+        }
+        if !before.is_empty() {
+            let nid = StoryId(self.alloc());
+            let mut ns = Story::new(nid);
+            ns.frames = before.clone();
+            for f in &before {
+                if let Some(t) = self.item_mut(*f).and_then(Item::text_frame_mut) {
+                    t.story = nid;
+                }
+            }
+            self.stories.insert(nid, Arc::new(ns));
+        }
         Ok(())
     }
 
+    /// [`Document::thread`], except that an empty `from` alone in its story, threaded in front of
+    /// the first frame of `to`'s story, joins that story: the story with the text keeps its id
+    /// (and whatever refers to it).
+    pub fn thread_keeping_story(&mut self, from: ItemId, to: ItemId) -> Result<()> {
+        let fs = self.frame_story(from)?;
+        let from_empty = fs.is_none_or(|fs| self.story(fs).is_some_and(|s| s.text.is_empty() && s.frames == [from]));
+        let ts = self.frame_story(to)?;
+        let to_first = ts.and_then(|ts| self.story(ts)).is_some_and(|s| s.frames.first() == Some(&to));
+        let (Some(ts), true, true) = (ts, from_empty, to_first && from != to) else { return self.thread(from, to) };
+        if let Some(fs) = fs {
+            self.stories.remove(&fs);
+        }
+        let st = self.story_mut(ts).ok_or(DocError::NoStory(ts))?;
+        st.frames.insert(0, from);
+        st.rev += 1;
+        let it = self.item_mut(from).ok_or(DocError::NoItem(from))?;
+        match it.text_frame_mut() {
+            Some(t) => t.story = ts,
+            None => it.content = Content::Text(TextFrame { story: ts, options: TextFrameOptions::default() }),
+        }
+        Ok(())
+    }
+
+    /// Can a user thread `from` → `to`? Both are text frames or empty frames (not lines), on
+    /// document spreads or on the same parent spread, not in one story already, and no frame
+    /// threads into `to` yet. [`Document::thread`] itself is less strict (import and autoflow).
+    pub fn check_thread(&self, from: ItemId, to: ItemId) -> Result<()> {
+        if from == to {
+            return Err(DocError::Invalid("cannot thread a frame to itself".into()));
+        }
+        for id in [from, to] {
+            let it = self.item(id).ok_or(DocError::NoItem(id))?;
+            if !matches!(it.content, Content::Text(_) | Content::Unassigned) || it.shape == Shape::GraphicLine {
+                return Err(DocError::Invalid(format!("{id} is not a text frame or an empty frame")));
+            }
+        }
+        let (Some(fl), Some(tl)) = (self.find(from), self.find(to)) else { return Err(DocError::NoItem(to)) };
+        let same_place = match (fl.spread, tl.spread) {
+            (SpreadRef::Doc(_), SpreadRef::Doc(_)) => true,
+            (a, b) => a == b,
+        };
+        if !same_place {
+            return Err(DocError::Invalid("frames on a parent spread thread only to frames on the same parent".into()));
+        }
+        let story = |id: ItemId| self.item(id).and_then(|i| i.text_frame()).map(|t| t.story);
+        if story(from).is_some() && story(from) == story(to) {
+            return Err(DocError::Invalid("the frames are already in the same thread".into()));
+        }
+        if self.prev_frame(to).is_some() {
+            return Err(DocError::Invalid(format!("text already flows into {to} from another frame: break that thread first")));
+        }
+        Ok(())
+    }
+
+    /// The story of a frame that can take part in a thread: `Some` for a text frame, `None` for
+    /// an empty (unassigned) frame.
+    fn frame_story(&self, id: ItemId) -> Result<Option<StoryId>> {
+        match &self.item(id).ok_or(DocError::NoItem(id))?.content {
+            Content::Text(t) => Ok(Some(t.story)),
+            Content::Unassigned => Ok(None),
+            _ => Err(DocError::Invalid("can only thread text frames or empty frames".into())),
+        }
+    }
+
+    /// Make an empty frame a text frame with a new empty story.
+    fn give_empty_story(&mut self, id: ItemId) -> Result<StoryId> {
+        let sid = StoryId(self.alloc());
+        let mut st = Story::new(sid);
+        st.frames.push(id);
+        let it = self.item_mut(id).ok_or(DocError::NoItem(id))?;
+        it.content = Content::Text(TextFrame { story: sid, options: TextFrameOptions::default() });
+        self.stories.insert(sid, Arc::new(st));
+        Ok(sid)
+    }
+
     /// Break the thread after `frame`: the following frames become a new empty story (the text
     /// stays with the first part and may become overset).
     pub fn unthread_after(&mut self, frame: ItemId) -> Result<()> {
@@ -298,6 +353,27 @@ impl Document {
         Ok(())
     }
 
+    /// Take `frame` out of its thread: the frames before and after it join up and keep the text,
+    /// `frame` stays on the page with a new empty story.
+    pub fn remove_from_thread(&mut self, frame: ItemId) -> Result<()> {
+        let sid = self.item(frame).and_then(|i| i.text_frame()).map(|t| t.story).ok_or(DocError::NoItem(frame))?;
+        {
+            let st = self.story_mut(sid).ok_or(DocError::NoStory(sid))?;
+            if st.frames.len() < 2 {
+                return Err(DocError::Invalid(format!("frame {frame} is not threaded to another frame")));
+            }
+            st.frames.retain(|f| *f != frame);
+            st.rev += 1;
+        }
+        let nid = StoryId(self.alloc());
+        let mut ns = Story::new(nid);
+        ns.frames = vec![frame];
+        self.stories.insert(nid, Arc::new(ns));
+        let t = self.item_mut(frame).and_then(Item::text_frame_mut).ok_or(DocError::NoItem(frame))?;
+        t.story = nid;
+        Ok(())
+    }
+
     /// Next / previous frame in a thread.
     pub fn next_frame(&self, frame: ItemId) -> Option<ItemId> {
         let st = self.story(self.item(frame)?.text_frame()?.story)?;
diff --git a/crates/doc/src/slice.rs b/crates/doc/src/slice.rs
index b376bf0e6..1d7067e8c 100644
--- a/crates/doc/src/slice.rs
+++ b/crates/doc/src/slice.rs
@@ -125,6 +125,59 @@ impl Story {
         self.rev += 1;
         end
     }
+
+    /// Append the whole of `other` as new paragraphs after this story's text (threading two
+    /// stories merges them this way). Its formatting, notes, endnotes, editorial notes, markers,
+    /// anchored objects and tables come along; footnotes, endnotes, editorial notes and tables get
+    /// ids that are free in this story. An empty story simply takes `other`'s content. Frames stay.
+    pub fn append_story(&mut self, mut other: Story) {
+        if other.text.is_empty() {
+            return;
+        }
+        if self.text.is_empty() {
+            let (id, frames, rev, link) = (self.id, std::mem::take(&mut self.frames), self.rev, self.link.take());
+            *self = Story { id, frames, rev: rev + 1, link, ..other };
+            return;
+        }
+        if !other.tables.is_empty() {
+            let first = self.tables.keys().max().copied().unwrap_or(0) + 1;
+            let mut ids = std::collections::HashMap::new();
+            for (new, (old, t)) in (first..).zip(std::mem::take(&mut other.tables)) {
+                let mut t = Arc::unwrap_or_clone(t);
+                t.id = new;
+                ids.insert(old, new);
+                self.tables.insert(new, Arc::new(t));
+            }
+            for p in &mut other.paras {
+                p.table = p.table.and_then(|id| ids.get(&id).copied());
+            }
+        }
+        self.text.push('\n');
+        self.text.push_str(&other.text);
+        // The paragraph end takes the last run's format.
+        if let Some(last) = self.chars.last_mut() {
+            last.len += 1;
+        }
+        self.chars.extend(other.chars.into_iter().filter(|r| r.len > 0));
+        self.paras.extend(other.paras);
+        for n in other.notes {
+            let id = self.next_note_id();
+            self.notes.push(Arc::new(crate::notes::Footnote { id, text: n.text.clone() }));
+        }
+        for n in other.endnotes {
+            let id = self.endnotes.iter().map(|x| x.id).max().unwrap_or(0) + 1;
+            self.endnotes.push(Arc::new(crate::notes::Footnote { id, text: n.text.clone() }));
+        }
+        for n in other.editorial {
+            let id = self.editorial.iter().map(|x| x.id).max().unwrap_or(0) + 1;
+            self.editorial.push(Arc::new(crate::endnotes::EditorialNote { id, ..(*n).clone() }));
+        }
+        self.anchors.extend(other.anchors);
+        self.xrefs.extend(other.xrefs);
+        self.index_refs.extend(other.index_refs);
+        self.objects.extend(other.objects);
+        self.rev += 1;
+    }
 }
 
 #[cfg(test)]
diff --git a/crates/doc/src/tests.rs b/crates/doc/src/tests.rs
index c3ba44dfd..e248d72eb 100644
--- a/crates/doc/src/tests.rs
+++ b/crates/doc/src/tests.rs
@@ -42,6 +42,98 @@ fn thread_to_empty_frame_converts_it() {
     assert!(d.thread(a, a).is_err());
 }
 
+#[test]
+fn threading_merges_tables_notes_and_endnotes() {
+    let mut d = doc();
+    let lid = d.default_layer();
+    let (a, sa) = d.add_text_frame(SpreadRef::Doc(0), Rect::new(10.0, 10.0, 100.0, 100.0), lid, "first", ParaFormat::default()).unwrap();
+    let (b, sb) = d.add_text_frame(SpreadRef::Doc(0), Rect::new(110.0, 10.0, 200.0, 100.0), lid, "second", ParaFormat::default()).unwrap();
+    for (sid, note) in [(sa, "Note A"), (sb, "Note B")] {
+        let st = d.story_mut(sid).unwrap();
+        st.insert_note(3, note, ParaFormat::default());
+        // Both stories hold a table with id 1.
+        let n = st.len();
+        st.insert_table(n, crate::table::Table::new(1, 2, 2, 0, 0, 80.0));
+    }
+    let st = d.story_mut(sb).unwrap();
+    st.insert_endnote(2, "End B", ParaFormat::default());
+    st.insert(1, &crate::NOTE_MARK.to_string());
+    d.thread(a, b).unwrap();
+    d.check().unwrap();
+    let st = d.story(sa).unwrap();
+    assert!(d.story(sb).is_none());
+    assert_eq!(st.tables.len(), 2);
+    assert_eq!(st.notes.len(), 2);
+    assert_eq!(st.notes[1].text.text, "Note B");
+    assert_eq!(st.endnotes.len(), 1);
+    assert_eq!(st.endnotes[0].text.text, "End B");
+    assert_eq!(st.editorial.len(), 1);
+}
+
+#[test]
+fn empty_frame_threaded_before_a_story_joins_it_at_the_front() {
+    let mut d = doc();
+    let lid = d.default_layer();
+    let (a, sa) = d.add_text_frame(SpreadRef::Doc(0), Rect::new(10.0, 10.0, 100.0, 100.0), lid, "", ParaFormat::default()).unwrap();
+    let (b, sb) = d.add_text_frame(SpreadRef::Doc(0), Rect::new(110.0, 10.0, 200.0, 100.0), lid, "Hello", ParaFormat::default()).unwrap();
+    d.thread_keeping_story(a, b).unwrap();
+    d.check().unwrap();
+    assert!(d.story(sa).is_none());
+    let st = d.story(sb).unwrap();
+    assert_eq!(st.frames, vec![a, b]);
+    assert_eq!(st.text, "Hello");
+}
+
+#[test]
+fn empty_story_takes_the_threaded_text_without_a_blank_paragraph() {
+    let mut d = doc();
+    let lid = d.default_layer();
+    let (a, _) = d.add_text_frame(SpreadRef::Doc(0), Rect::new(10.0, 10.0, 100.0, 100.0), lid, "", ParaFormat::default()).unwrap();
+    let (a2, _) = d.add_text_frame(SpreadRef::Doc(0), Rect::new(10.0, 110.0, 100.0, 200.0), lid, "", ParaFormat::default()).unwrap();
+    d.thread(a, a2).unwrap();
+    let (b, _) = d.add_text_frame(SpreadRef::Doc(0), Rect::new(110.0, 10.0, 200.0, 100.0), lid, "Hello", ParaFormat::default()).unwrap();
+    d.thread(a2, b).unwrap();
+    d.check().unwrap();
+    let st = d.story(d.item(a).unwrap().text_frame().unwrap().story).unwrap();
+    assert_eq!(st.frames, vec![a, a2, b]);
+    assert_eq!(st.text, "Hello");
+}
+
+#[test]
+fn threading_from_an_empty_frame_makes_it_a_text_frame() {
+    let mut d = doc();
+    let lid = d.default_layer();
+    let id = ItemId(d.alloc());
+    let it = Item::new(id, lid, Shape::Rectangle, designcraft_geom::shapes::rectangle(Rect::new(0.0, 200.0, 50.0, 300.0)));
+    d.insert_item(SpreadRef::Doc(0), it, None).unwrap();
+    let (b, _) = d.add_text_frame(SpreadRef::Doc(0), Rect::new(110.0, 10.0, 200.0, 100.0), lid, "Hello", ParaFormat::default()).unwrap();
+    d.thread(id, b).unwrap();
+    d.check().unwrap();
+    let st = d.story(d.item(id).unwrap().text_frame().unwrap().story).unwrap();
+    assert_eq!(st.frames, vec![id, b]);
+    assert_eq!(st.text, "Hello");
+}
+
+#[test]
+fn removing_a_frame_from_its_thread_keeps_the_text_in_the_others() {
+    let mut d = doc();
+    let lid = d.default_layer();
+    let (a, sa) = d.add_text_frame(SpreadRef::Doc(0), Rect::new(10.0, 10.0, 100.0, 100.0), lid, "words", ParaFormat::default()).unwrap();
+    let (b, _) = d.add_text_frame(SpreadRef::Doc(0), Rect::new(110.0, 10.0, 200.0, 100.0), lid, "", ParaFormat::default()).unwrap();
+    let (c, _) = d.add_text_frame(SpreadRef::Doc(0), Rect::new(210.0, 10.0, 300.0, 100.0), lid, "", ParaFormat::default()).unwrap();
+    d.thread(a, b).unwrap();
+    d.thread(b, c).unwrap();
+    d.remove_from_thread(b).unwrap();
+    d.check().unwrap();
+    assert_eq!(d.story(sa).unwrap().frames, vec![a, c]);
+    assert_eq!(d.story(sa).unwrap().text, "words");
+    let own = d.item(b).unwrap().text_frame().unwrap().story;
+    assert_ne!(own, sa);
+    assert!(d.story(own).unwrap().text.is_empty());
+    // A frame alone in its story has no thread to leave.
+    assert!(d.remove_from_thread(b).is_err());
+}
+
 #[test]
 fn removing_last_frame_deletes_story() {
     let mut d = doc();
diff --git a/crates/engine/src/cmd/mod.rs b/crates/engine/src/cmd/mod.rs
index 941473561..6413445c9 100644
--- a/crates/engine/src/cmd/mod.rs
+++ b/crates/engine/src/cmd/mod.rs
@@ -50,6 +50,7 @@ mod strokes;
 mod style;
 pub mod table;
 pub mod text;
+mod thread;
 mod toc;
 mod transitions;
 mod variables;
@@ -184,6 +185,7 @@ pub fn command_specs() -> &'static [CommandSpec] {
         v.extend(package::specs());
         v.extend(print::specs());
         v.extend(text::specs());
+        v.extend(thread::specs());
         v.extend(style::specs());
         v.extend(table::specs());
         v.extend(layout::specs());
diff --git a/crates/engine/src/cmd/thread.rs b/crates/engine/src/cmd/thread.rs
new file mode 100644
index 000000000..ff360e00a
--- /dev/null
+++ b/crates/engine/src/cmd/thread.rs
@@ -0,0 +1,335 @@
+//! Threading text frames: thread a frame after another (their stories merge), break a thread,
+//! take a frame out of its thread. The Selection tool's loaded text cursor runs these.
+
+use designcraft_doc::{Document, ItemId, ParaFormat, Selection, StoryId};
+use designcraft_geom::Rect;
+use serde_json::{Value, json};
+
+use super::{CommandSpec, bad, bool_or, cmd, has_doc, id_param, rect_param, spread_param, str_param};
+use crate::{Result, Session};
+
+/// Pages Shift-click autoflow may add before it gives up.
+const AUTOFLOW_MAX_PAGES: usize = 2000;
+
+pub fn specs() -> Vec<CommandSpec> {
+    vec![
+        cmd!(
+            "text.thread",
+            "Thread Text Frames",
+            [],
+            None,
+            "{from?, to?, rect?: [x0,y0,x1,y1] (spread coords), spread?, autoflow?: bool} — threads frame `to` right after frame `from` (between `from` and the frame that followed it, if any). `to` is an empty frame or a text frame nothing threads into yet; its text joins the end of the story. Give `rect` in place of `from` or `to` to thread a new text frame made there on `spread`: `{from, rect}` adds it after `from`, `{rect, to}` in front of `to`. autoflow: then add pages with threaded frames until the story fits. Selects the frame that joined the thread. → {story, from, to, overset, pagesAdded}",
+            has_doc,
+            thread
+        ),
+        cmd!(
+            "text.unthread",
+            "Break Thread",
+            [],
+            None,
+            "{frame?, side?: after|before} — breaks the thread after (or before) `frame` (default: the selected text frame). The frames from the break on stay threaded to each other but become empty; the text stays in the story, overset if the earlier frames can't hold it",
+            has_doc,
+            unthread
+        ),
+        cmd!(
+            "text.removeFromThread",
+            "Remove Frame from Thread",
+            [],
+            None,
+            "{frame?} — takes `frame` (default: the selected text frame) out of its thread: the frames before and after it join up and keep the text, `frame` stays empty",
+            has_doc,
+            remove_from_thread
+        ),
+    ]
+}
+
+/// `frame` param, or the first selected text frame.
+fn frame_param(s: &Session, p: &Value, cmd: &str) -> Result<ItemId> {
+    let st = s.doc()?;
+    let id = id_param(p, "frame")
+        .or_else(|| st.selection.items.iter().copied().find(|i| st.doc.item(*i).is_some_and(|it| it.is_text_frame())))
+        .ok_or_else(|| bad(cmd, "no text frame given or selected"))?;
+    if !st.doc.item(id).is_some_and(|it| it.is_text_frame()) {
+        return Err(bad(cmd, format!("{id} is not a text frame")));
+    }
+    Ok(id)
+}
+
+/// A rect param made safe for a frame: finite, ordered, at least half a point each way.
+fn frame_rect(p: &Value) -> Result<Option<Rect>> {
+    let Some(r) = rect_param(p, "rect") else { return Ok(None) };
+    if ![r.x0, r.y0, r.x1, r.y1].iter().all(|v| v.is_finite()) {
+        return Err(bad("text.thread", "rect must be finite"));
+    }
+    let (x0, x1) = (r.x0.min(r.x1), r.x0.max(r.x1));
+    let (y0, y1) = (r.y0.min(r.y1), r.y0.max(r.y1));
+    Ok(Some(Rect::new(x0, y0, x1.max(x0 + 0.5), y1.max(y0 + 0.5))))
+}
+
+fn thread(s: &mut Session, p: &Value) -> Result<Value> {
+    let (from, to, rect) = (id_param(p, "from"), id_param(p, "to"), frame_rect(p)?);
+    let sr = spread_param(p, "spread");
+    let autoflow = bool_or(p, "autoflow", false);
+    let layer = s.doc()?.active_layer;
+    s.edit(|d, sel| {
+        let mut new_frame = || -> Result<ItemId> {
+            let r = rect.ok_or_else(|| bad("text.thread", "give two of from, to and rect"))?;
+            let para = ParaFormat { style: d.styles.default_paragraph.clone(), ..Default::default() };
+            Ok(d.add_text_frame(sr, r, layer, "", para)?.0)
+        };
+        let (from, to, joined) = match (from, to) {
+            (Some(f), Some(t)) if rect.is_none() => (f, t, t),
+            (Some(f), None) => {
+                let t = new_frame()?;
+                (f, t, t)
+            }
+            (None, Some(t)) => {
+                let f = new_frame()?;
+                (f, t, f)
+            }
+            _ => return Err(bad("text.thread", "give two of from, to and rect")),
+        };
+        d.check_thread(from, to)?;
+        d.thread_keeping_story(from, to)?;
+        let sid = d.item(from).and_then(|i| i.text_frame()).map(|t| t.story).ok_or_else(|| bad("text.thread", "threading lost the story"))?;
+        let pages = if autoflow { super::place_text_autoflow(d, sid, AUTOFLOW_MAX_PAGES)? } else { 0 };
+        *sel = Selection::items(vec![joined]);
+        Ok(json!({"story": sid.0, "from": from.0, "to": to.0, "overset": overset(d, sid), "pagesAdded": pages}))
+    })
+}
+
+fn overset(d: &Document, sid: StoryId) -> bool {
+    designcraft_compose::compose_story(d, sid, &Default::default()).overset_at.is_some()
+}
+
+fn unthread(s: &mut Session, p: &Value) -> Result<Value> {
+    const CMD: &str = "text.unthread";
+    let frame = frame_param(s, p, CMD)?;
+    let d0 = &s.doc()?.doc;
+    let at = match str_param(p, "side").unwrap_or("after") {
+        "after" => d0.next_frame(frame).map(|_| frame).ok_or_else(|| bad(CMD, format!("no frame follows {frame} in its thread")))?,
+        "before" => d0.prev_frame(frame).ok_or_else(|| bad(CMD, format!("no frame comes before {frame} in its thread")))?,
+        other => return Err(bad(CMD, format!("unknown side `{other}` (after, before)"))),
+    };
+    s.edit(|d, _| {
+        d.unthread_after(at)?;
+        let sid = d.item(at).and_then(|i| i.text_frame()).map(|t| t.story).ok_or_else(|| bad(CMD, "no story"))?;
+        Ok(json!({"story": sid.0, "overset": overset(d, sid)}))
+    })
+}
+
+fn remove_from_thread(s: &mut Session, p: &Value) -> Result<Value> {
+    let frame = frame_param(s, p, "text.removeFromThread")?;
+    s.edit(|d, _| {
+        d.remove_from_thread(frame)?;
+        Ok(json!({}))
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use serde_json::json;
+
+    use crate::Session;
+
+    fn session() -> Session {
+        let mut s = Session::new();
+        s.execute("file.new", &json!({"pages": 2})).unwrap();
+        s
+    }
+
+    fn text_frame(s: &mut Session, rect: [f64; 4], text: &str) -> (u64, u64) {
+        let r = s.execute("frame.create", &json!({"rect": rect, "content": "text", "text": text, "caret": false})).unwrap();
+        (r["id"].as_u64().unwrap(), r["story"].as_u64().unwrap())
+    }
+
+    fn story(s: &mut Session, frame: u64) -> serde_json::Value {
+        s.execute("story.get", &json!({"frame": frame})).unwrap()
+    }
+
+    fn frames(s: &mut Session, frame: u64) -> Vec<u64> {
+        story(s, frame)["frames"].as_array().unwrap().iter().map(|v| v.as_u64().unwrap()).collect()
+    }
+
+    const LONG: &str = "Threaded text keeps flowing from one frame into the next one. ";
+
+    #[test]
+    fn thread_into_an_empty_frame_and_undo() {
+        let mut s = session();
+        let (a, sid) = text_frame(&mut s, [72.0, 72.0, 200.0, 120.0], &LONG.repeat(10));
+        let b = s.execute("frame.create", &json!({"rect": [72, 300, 200, 400], "content": "unassigned"})).unwrap()["id"].as_u64().unwrap();
+        assert!(!story(&mut s, a)["overset"].is_null(), "the first frame is overset");
+        let r = s.execute("text.thread", &json!({"from": a, "to": b})).unwrap();
+        assert_eq!(r["story"].as_u64(), Some(sid));
+        assert_eq!(frames(&mut s, a), [a, b]);
+        let d = &s.doc().unwrap().doc;
+        assert!(d.item(designcraft_doc::ItemId(b)).unwrap().is_text_frame());
+        assert_eq!(s.doc().unwrap().selection.items, [designcraft_doc::ItemId(b)]);
+        // The text now reaches the second frame.
+        let cs = designcraft_compose::compose_story(&s.doc().unwrap().doc, designcraft_doc::StoryId(sid), &Default::default());
+        assert!(cs.frames.iter().any(|f| f.frame.0 == b && !f.range.is_empty()), "text flows into the new frame");
+        s.doc().unwrap().doc.check().unwrap();
+        s.execute("edit.undo", &json!({})).unwrap();
+        assert_eq!(frames(&mut s, a), [a]);
+        assert!(!s.doc().unwrap().doc.item(designcraft_doc::ItemId(b)).unwrap().is_text_frame());
+    }
+
+    #[test]
+    fn thread_into_a_text_frame_merges_its_story() {
+        let mut s = session();
+        let (a, sa) = text_frame(&mut s, [72.0, 72.0, 200.0, 200.0], "First");
+        let (b, sb) = text_frame(&mut s, [72.0, 300.0, 200.0, 400.0], "Second");
+        s.execute("text.thread", &json!({"from": a, "to": b})).unwrap();
+        let st = story(&mut s, b);
+        assert_eq!(st["id"].as_u64(), Some(sa));
+        assert_eq!(st["text"], "First\nSecond");
+        assert!(s.doc().unwrap().doc.story(designcraft_doc::StoryId(sb)).is_none());
+        s.doc().unwrap().doc.check().unwrap();
+    }
+
+    #[test]
+    fn thread_into_the_middle_of_a_thread() {
+        let mut s = session();
+        let (a, _) = text_frame(&mut s, [72.0, 72.0, 200.0, 120.0], &LONG.repeat(8));
+        let (c, _) = text_frame(&mut s, [72.0, 500.0, 200.0, 600.0], "");
+        s.execute("text.thread", &json!({"from": a, "to": c})).unwrap();
+        let (b, _) = text_frame(&mut s, [72.0, 300.0, 200.0, 400.0], "");
+        s.execute("text.thread", &json!({"from": a, "to": b})).unwrap();
+        assert_eq!(frames(&mut s, a), [a, b, c]);
+        s.doc().unwrap().doc.check().unwrap();
+    }
+
+    #[test]
+    fn bad_threads_are_errors_and_change_nothing() {
+        let mut s = session();
+        let (a, _) = text_frame(&mut s, [72.0, 72.0, 200.0, 120.0], "a");
+        let (b, _) = text_frame(&mut s, [72.0, 300.0, 200.0, 400.0], "b");
+        let (x, _) = text_frame(&mut s, [300.0, 72.0, 400.0, 120.0], "x");
+        let (y, _) = text_frame(&mut s, [300.0, 300.0, 400.0, 400.0], "y");
+        let g = s.execute("line.create", &json!({"a": [300, 500], "b": [400, 600]})).unwrap()["id"].as_u64().unwrap();
+        let group = {
+            let p = s.execute("frame.create", &json!({"rect": [500, 500, 550, 550], "content": "unassigned"})).unwrap()["id"].clone();
+            let q = s.execute("frame.create", &json!({"rect": [560, 500, 600, 550], "content": "unassigned"})).unwrap()["id"].clone();
+            s.execute("selection.set", &json!({"ids": [p, q]})).unwrap();
+            s.execute("object.group", &json!({})).unwrap();
+            s.doc().unwrap().selection.items[0].0
+        };
+        s.execute("text.thread", &json!({"from": a, "to": b})).unwrap();
+        s.execute("text.thread", &json!({"from": x, "to": y})).unwrap();
+        let undo = s.doc().unwrap().history.undo.len();
+        let doc = s.doc().unwrap().doc.clone();
+        for p in [
+            json!({"from": a, "to": a}),
+            json!({"from": a, "to": g}),
+            json!({"from": g, "to": a}),
+            json!({"from": a, "to": group}),
+            // Earlier in the same thread.
+            json!({"from": b, "to": a}),
+            // Text already flows into y from x.
+            json!({"from": a, "to": y}),
+            json!({"from": a, "to": 999_999}),
+            json!({"from": a}),
+            json!({"from": a, "to": b, "rect": [0, 0, 10, 10]}),
+            json!({"rect": [0, 0, 10, 10]}),
+            json!({"from": a, "rect": [0, 0, 10, 10], "spread": 99}),
+            json!({"from": "a", "to": [1]}),
+            json!([1, 2]),
+        ] {
+            assert!(s.execute("text.thread", &p).is_err(), "{p}");
+        }
+        assert_eq!(s.doc().unwrap().history.undo.len(), undo);
+        assert_eq!(*s.doc().unwrap().doc, *doc);
+    }
+
+    #[test]
+    fn thread_a_new_frame_after_or_in_front() {
+        let mut s = session();
+        let (a, sa) = text_frame(&mut s, [72.0, 72.0, 200.0, 120.0], &LONG.repeat(8));
+        let r = s.execute("text.thread", &json!({"from": a, "rect": [72, 300, 200, 400]})).unwrap();
+        let n = r["to"].as_u64().unwrap();
+        assert_eq!(frames(&mut s, a), [a, n]);
+        assert_eq!(s.doc().unwrap().selection.items, [designcraft_doc::ItemId(n)]);
+        let b = s.doc().unwrap().doc.item(designcraft_doc::ItemId(n)).unwrap().bounds();
+        assert_eq!(b, Rect::new(72.0, 300.0, 200.0, 400.0));
+        // In front of the first frame: the story keeps its id and text.
+        let r = s.execute("text.thread", &json!({"rect": [300, 72, 400, 120], "to": a})).unwrap();
+        let m = r["from"].as_u64().unwrap();
+        assert_eq!(r["story"].as_u64(), Some(sa));
+        assert_eq!(frames(&mut s, a), [m, a, n]);
+        assert_eq!(story(&mut s, a)["text"], LONG.repeat(8));
+        s.doc().unwrap().doc.check().unwrap();
+        // One undo step each.
+        s.execute("edit.undo", &json!({})).unwrap();
+        assert_eq!(frames(&mut s, a), [a, n]);
+    }
+
+    use designcraft_geom::Rect;
+
+    #[test]
+    fn thread_with_autoflow_adds_pages_until_the_text_fits() {
+        let mut s = session();
+        let (a, _) = text_frame(&mut s, [72.0, 72.0, 300.0, 200.0], &LONG.repeat(300));
+        let r = s.execute("text.thread", &json!({"from": a, "rect": [72, 300, 300, 700], "autoflow": true})).unwrap();
+        assert_eq!(r["overset"], false);
+        assert!(r["pagesAdded"].as_u64().unwrap() >= 1, "{r}");
+        assert!(frames(&mut s, a).len() >= 3);
+        s.doc().unwrap().doc.check().unwrap();
+        // One undo removes the frames and the pages.
+        s.execute("edit.undo", &json!({})).unwrap();
+        assert_eq!(frames(&mut s, a), [a]);
+        assert_eq!(s.doc().unwrap().doc.page_count(), 2);
+    }
+
+    #[test]
+    fn unthread_after_and_before() {
+        let mut s = session();
+        let text = LONG.repeat(12);
+        let (a, sa) = text_frame(&mut s, [72.0, 72.0, 200.0, 120.0], &text);
+        let (b, _) = text_frame(&mut s, [72.0, 200.0, 200.0, 250.0], "");
+        let (c, _) = text_frame(&mut s, [72.0, 300.0, 200.0, 350.0], "");
+        s.execute("text.thread", &json!({"from": a, "to": b})).unwrap();
+        s.execute("text.thread", &json!({"from": b, "to": c})).unwrap();
+        // Break after the first frame: b and c stay threaded to each other, empty.
+        let r = s.execute("text.unthread", &json!({"frame": a})).unwrap();
+        assert_eq!(r["story"].as_u64(), Some(sa));
+        assert_eq!(r["overset"], true);
+        assert_eq!(frames(&mut s, a), [a]);
+        assert_eq!(story(&mut s, a)["text"], text);
+        assert_eq!(frames(&mut s, b), [b, c]);
+        assert_eq!(story(&mut s, b)["text"], "");
+        s.doc().unwrap().doc.check().unwrap();
+        s.execute("edit.undo", &json!({})).unwrap();
+        assert_eq!(frames(&mut s, a), [a, b, c]);
+        // Break before the last frame, with the frame selected.
+        s.execute("selection.set", &json!({"ids": [c]})).unwrap();
+        s.execute("text.unthread", &json!({"side": "before"})).unwrap();
+        assert_eq!(frames(&mut s, a), [a, b]);
+        assert_eq!(frames(&mut s, c), [c]);
+        // Nothing to break.
+        assert!(s.execute("text.unthread", &json!({"frame": b})).is_err());
+        assert!(s.execute("text.unthread", &json!({"frame": a, "side": "before"})).is_err());
+        assert!(s.execute("text.unthread", &json!({"frame": a, "side": "sideways"})).is_err());
+        assert!(s.execute("text.unthread", &json!({"frame": 999_999})).is_err());
+    }
+
+    #[test]
+    fn deleting_or_removing_a_threaded_frame_keeps_the_text_flowing() {
+        let mut s = session();
+        let text = LONG.repeat(12);
+        let (a, _) = text_frame(&mut s, [72.0, 72.0, 200.0, 120.0], &text);
+        let (b, _) = text_frame(&mut s, [72.0, 200.0, 200.0, 250.0], "");
+        let (c, _) = text_frame(&mut s, [72.0, 300.0, 200.0, 350.0], "");
+        s.execute("text.thread", &json!({"from": a, "to": b})).unwrap();
+        s.execute("text.thread", &json!({"from": b, "to": c})).unwrap();
+        s.execute("text.removeFromThread", &json!({"frame": b})).unwrap();
+        assert_eq!(frames(&mut s, a), [a, c]);
+        assert_eq!(story(&mut s, a)["text"], text);
+        assert_eq!(story(&mut s, b)["text"], "");
+        assert!(s.execute("text.removeFromThread", &json!({"frame": b})).is_err());
+        s.execute("edit.undo", &json!({})).unwrap();
+        s.execute("edit.clear", &json!({"ids": [b]})).unwrap();
+        assert_eq!(frames(&mut s, a), [a, c]);
+        assert_eq!(story(&mut s, a)["text"], text);
+        s.doc().unwrap().doc.check().unwrap();
+    }
+}