Illustrator links type in an area or along a path (https://helpx.adobe.com/illustrator/using/manage-text-area.html); until now only area type threaded here. Type on a path that overflows ends its line where its text stops fitting, so a story flows on from it, and its red out port, just past its end bracket, loads the Selection tool with the text as area type's does. A new frame threaded from it at a point is type on a path of its shape.
Document symbols placed inline in a run of type (beyond Illustrator; like
InDesign inline anchored objects): TextRun.inline holds the symbol, scale and
shift; the run is one U+FFFC laid out as a glyph sized to the art, centred on
the cap height. text.insertInline and Type > Insert Inline Symbol; editing
keeps the graphic whole; canvas, SVG (<use>) and PDF draw the art; Create
Outlines turns it into a symbol instance.
Each paragraph has its own alignment, indents, spacing, hyphenation, tab
stops and paragraph style (TextObject.paras; para stays paragraph 0's, so
old files and readers work). Layout, editing (split/merge), threads, the
Paragraph/Tabs/Paragraph Styles panels, ranged text.setStyle/setFormat/
tabs/paraStyle.apply, SVG export/import and the fuzzers follow.
Jürg Lehni