Glyph alternates: read tag=0 as off in the OpenType dialog; one accurate doc statement of how alternates apply

docs/type-parity.md

@@ -30,8 +30,8 @@ against Illustrator's public documentation; **estimated** unless noted.
 | Copy or Cut selected characters, then paste as separate text art | done | A Type-range copy keeps the selected characters' font family, size and color when pasted on the canvas after leaving text editing, in the same document or another. On desktop the clipboard offers plain text to text consumers and rich art for canvas Paste; Paste Without Formatting while editing uses the destination text's style. `tests::clipboard::type_range_copy_stays_styled_when_pasted_as_art` (#5636) |
 | Character size and horizontal scale after object/group scaling | done | #1034: fields and setters compensate the stored affine; point size follows the transformed em-height axis, not the glyph ink bounds. Range edits, keyboard increments, leading and baseline shift use document points; rotation, reflection and shear remain editable. |
 | Preserve font sizes while scaling a group | missing | Separate enhancement; scaling still scales text with the other artwork. |
-| OpenType panel, Glyphs panel, alternates | done | Highlight Alternate Glyphs preference (#394, off by default) paints pink behind OpenType substitutions on screen when on (required shaping such as Arabic joining forms and the lam-alef ligature, including a lam-alef older fonts file under `liga`, is not highlighted; an optional feature that changes the ligature is); stylistic sets ss01–ss20, stylistic and titling alternates, proportional and lining figures, superscript and subscript are character-style features (`text.setStyle {features}`, #1607); the OpenType panel's Position menu sets superscript, subscript, numerator or denominator glyphs (`sups`, `subs`, `numr`, `dnom`). The OpenType panel's Stylistic Sets menu lists the selected font's `ss01`–`ss20` features, using a font-supplied name where available and `Set N` otherwise; several sets can be active, and selecting an active one removes it. For a mixed-font selection it uses the first selected character's font, a VectorCraft design choice ([public help](https://helpx.adobe.com/illustrator/desktop/design-with-text/special-characters-glyphs/add-stylistic-sets-to-selected-text.html), [OpenType feature specification](https://learn.microsoft.com/en-us/typography/opentype/spec/features_pt)). The Glyphs panel highlights the character selected with the Type tool (a range's first character, else the one before the caret) and scrolls it into view as the selection moves (#4908; `panels::glyphs` tests); its Show menu lists Unicode ranges and Alternates for Current Selection, the selected character's alternate glyphs from the font's `GSUB` table, one of which a double-click draws for that character (`text.setGlyphAlternate`); the glyph-cell pop-up of alternates is not there yet |
-| Glyphs panel: alternates as OpenType feature values, unencoded glyphs | done | #5514, as [Replace characters with alternate glyphs](https://helpx.adobe.com/illustrator/desktop/design-with-text/special-characters-glyphs/replace-characters-with-alternate-glyphs.html) describes (Show › Alternates For Current Selection; replace the selected character by double-clicking the glyph). A character-style feature takes a value (`"salt=2"`, the font's alternate number; `ss01`–`ss20`, `swsh`, `titl` and `aalt` too) in `features` and `featureChanges`, in SVG `font-feature-settings` (`"salt" 2`) and in native files as the plain string. Show › Entire Font applies an unencoded glyph the same way when it is an alternate of the selected character in its word, and dims the others with the reason in the tooltip (e.g. `yehfarsi.fina.alt2 belongs to ی (U+06CC) at the end of a word; your selection is ي (U+064A)`); an Arabic presentation form picked there inserts its letter so the word joins. Runs that differ only in their features shape as one piece of text, each run's features over its own characters, so a variant on one letter of an Arabic word keeps its neighbours' initial, medial and final forms and the letters still touch. The panel lists the alternates of the glyph the shaper makes for the selected character in its word (a medial letter shows medial variants), and a double-click applies the feature that draws the variant to that character alone, in one undo step (`text.setRangeStyle`); a variant no feature draws there is drawn as a replacement glyph (`text.setGlyphAlternate`), which its tooltip says may not join. Show › Entire Font also lists the glyphs no character maps, with their name or `gid N` and the feature that gives them. The text crate reads each face's `GSUB` once (alternate sets, single substitutions, the feature that reaches a glyph). Not done: alternates reached through contextual or ligature lookups, and features of the font that the style has no tag for (`cv01`–`cv99`, `hist`). Evidence: `tests::glyph_alternates` in the text crate (a fixture font with a medial teh at `salt=1` to `3`, the neighbours' forms, no gap; Kufi Murabba PIIIX when it is installed), `features::tests::feature_values_are_parsed_validated_and_shaped`, `tests::textedit::feature_values_are_set_replaced_and_saved`, the `panels::glyphs` tests. |
+| OpenType panel, Glyphs panel, alternates | done | Highlight Alternate Glyphs preference (#394, off by default) paints pink behind OpenType substitutions on screen when on (required shaping such as Arabic joining forms and the lam-alef ligature, including a lam-alef older fonts file under `liga`, is not highlighted; an optional feature that changes the ligature is); stylistic sets ss01–ss20, stylistic and titling alternates, proportional and lining figures, superscript and subscript are character-style features (`text.setStyle {features}`, #1607); the OpenType panel's Position menu sets superscript, subscript, numerator or denominator glyphs (`sups`, `subs`, `numr`, `dnom`). The OpenType panel's Stylistic Sets menu lists the selected font's `ss01`–`ss20` features, using a font-supplied name where available and `Set N` otherwise; several sets can be active, and selecting an active one removes it. For a mixed-font selection it uses the first selected character's font, a VectorCraft design choice ([public help](https://helpx.adobe.com/illustrator/desktop/design-with-text/special-characters-glyphs/add-stylistic-sets-to-selected-text.html), [OpenType feature specification](https://learn.microsoft.com/en-us/typography/opentype/spec/features_pt)). The Glyphs panel highlights the character selected with the Type tool (a range's first character, else the one before the caret) and scrolls it into view as the selection moves (#4908; `panels::glyphs` tests); its Show menu lists Unicode ranges and Alternates for Current Selection, the selected character's alternate glyphs from the font's `GSUB` table, a double-click applies the OpenType feature that draws one (`salt=N`, `ssNN`) to that character alone; a variant no feature reaches is drawn through `text.setGlyphAlternate`, which may not join; Show › Entire Font applies the selected letter's alternates the same way and dims the others with the reason; the glyph-cell pop-up of alternates is not there yet |
+| Glyphs panel: alternates as OpenType feature values, unencoded glyphs | done | #5514, as [Replace characters with alternate glyphs](https://helpx.adobe.com/illustrator/desktop/design-with-text/special-characters-glyphs/replace-characters-with-alternate-glyphs.html) describes (Show › Alternates For Current Selection; replace the selected character by double-clicking the glyph). A character-style feature takes a value (`"salt=2"`, the font's alternate number; `ss01`–`ss20`, `swsh`, `titl` and `aalt` too) in `features` and `featureChanges`, in SVG `font-feature-settings` (`"salt" 2`) and in native files as the plain string. Show › Entire Font applies an unencoded glyph the same way when it is an alternate of the selected character in its word, and dims the others with the reason in the tooltip (e.g. `yehfarsi.fina.alt2 belongs to ی (U+06CC) at the end of a word; your selection is ي (U+064A)`); an Arabic presentation form picked there inserts its letter so the word joins. Runs that differ only in their features shape as one piece of text, each run's features over its own characters, so a variant on one letter of an Arabic word keeps its neighbours' initial, medial and final forms and the letters still touch. The panel lists the alternates of the glyph the shaper makes for the selected character in its word (a medial letter shows medial variants), and a double-click applies the OpenType feature that draws the variant (`salt=N` or `ssNN`) to that character alone, in one undo step (`text.setRangeStyle`); a variant no feature reaches falls back to a replacement glyph (`text.setGlyphAlternate`), which its tooltip says may not join. Show › Entire Font also lists the glyphs no character maps, with their name or `gid N` and the feature that gives them. The text crate reads each face's `GSUB` once (alternate sets, single substitutions, the feature that reaches a glyph). Not done: alternates reached through contextual or ligature lookups, and features of the font that the style has no tag for (`cv01`–`cv99`, `hist`). Evidence: `tests::glyph_alternates` in the text crate (a fixture font with a medial teh at `salt=1` to `3`, the neighbours' forms, no gap; Kufi Murabba PIIIX when it is installed), `features::tests::feature_values_are_parsed_validated_and_shaped`, `tests::textedit::feature_values_are_set_replaced_and_saved`, the `panels::glyphs` tests. |
 | Font menu: samples, live preview, filters, favourites, recent families; font matching by any name; Find Font | done | #3515: recently applied families appear first, once each; missing families are omitted and the existing Number of Recent Fonts setting applies; #339; script filter: Japanese, Latin, Thai; the font scan on Linux also reads the folders fontconfig's configuration lists, such as TeX fonts under `/usr/share/texmf/fonts` (#1548, fixes #1529; not verified on Linux)  Replace With Font lists family and style rows, one click setting both, with a search over them; its list scrolls on its own, apart from the document's font list (#4972). |
 | Missing glyphs set in an installed font made for their script (Thai, Lao, Khmer, Myanmar first; then any font that has them) | done | Thai: Leelawadee UI, Tahoma, Thonburi, Sukhumvit Set, Noto Sans Thai, TLWG |
 | Full font-name matching (OpenType name ID 4) | done | #1258: loaded/cataloged faces and Missing Fonts searches; localized names and variable default faces; Windows font-service QA pending |