Set Anchors adds the anchors a glyph needs for mark positioning and Auto Attach, placed from the glyph's own outline. It knows which anchors a letter of a given script should carry (a top and a bottom anchor on a Latin base, the matching _top and _bottom on a mark, one anchor per component on a ligature, and so on) and where each belongs: a top anchor centred on the letter's optical centre at the x-height, cap height or a higher line, a bottom anchor on the baseline, with the lines it measures against coming from the font's alignment metrics.

Select one or more glyphs in the Font Overview, or work in the glyph editor, and choose Glyph > Set Anchors (Ctrl+U, Cmd+U on macOS). Anchors the glyph already has are left exactly where they are; only the missing ones are added. Glyph > Recalculate Anchors (Ctrl+Shift+U) resets the anchors it knows about to their computed positions and adds the missing ones; anchors with other names, such as a font's own private ones or cursive entry and exit anchors, are never touched by either command. Both are one undo step.

What it learns from the font

Before placing anything, Set Anchors measures the anchors the font already has, class by class, and compares them with where its own rules would put them. Where the font is consistent about a difference, and adopting it would improve the placement of the anchors it was not learned from, that difference is adopted, so the new anchors follow the house convention rather than a generic one. At least three anchors have to agree before a convention is learned. Fonts that name their anchors differently (markAbove and markBelow, TashkilAbove and TashkilBelow) are read as well.

Masters

With Edit Across Layers on, both commands write every master, each from that master's own outline. With it off, they write only the master you are working on; Set Anchors then also turns anchors that this master was only showing as interpolated values into real anchors on that master, at the position they had, so you can edit them there. Intermediate masters get their own anchors too, measured against metric lines interpolated at that master's position. When no master is active (the variation sliders between masters), the commands say so and stop.

Scripts and roles

The placement rules are per script: Latin, Greek, Cyrillic, Hebrew, Arabic and others each have their own. A script whose marks sit on one shared line across the alphabet, such as Hebrew, gets that line from an alignment metric with the role Anchor top (or Anchor bottom) scoped to the script; see Alignment Metrics. Without such a line, the x-height, cap height and baseline are used.

After Set Anchors

Use Auto Attach or Complete Composites to build the composites from the anchors, and the Anchor Manager to generate the mark positioning lookups. The Anchors panel lists the anchors of the active glyph.