With View › Snap to Glyph and Smart Guides on, a point drawn near a single
line of live type now also lands on the anchor points of its glyphs and lines
up with its x-height (raised or lowered by Baseline Shift) and with the edges
of each character's advance width along the baseline (proximity guides). In
rotated type the baseline, x-height and proximity guides run at the type's
angle, and type of one glyph also has angular guides along the glyph's slanted
straight segments; a segment that Shift keeps to its angle slides onto them.
A paragraph shows glyph bounds only, so its baselines are no longer guides.
FontFace::x_height gives a face's x-height in font units.
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