Parity: the Text Frame Options Preview with an invalid value, spelt out

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/target-app-parity.md

@@ -343,7 +343,7 @@ It is evidence of breadth: each item exists. It is not a claim of InDesign-level
 - Column rules (Text Frame Options › Column Rules, `object.textFrameOptions {columnRule, columnRuleWeight, columnRuleColor, columnRuleTint, columnRuleOffset, columnRuleTopInset, columnRuleBottomInset}`, reported by `document.inspect`): a bar centred in each gutter of a multi-column frame, inside the insets and between the columns of right-to-left and vertical frames too, broken around paragraphs that span columns, with weight, colour, tint, horizontal offset and top/bottom insets; on screen, in PDF (tagged as an artifact) and in IDML (`ColumnRule…` attributes of `TextFramePreference`, also in object styles). The dialog shows the frame's options and changes only the fields edited. Rule stroke types and overprint aren't there yet.
 - Auto-size (Text Frame Options › Auto-Size, `object.textFrameOptions {autoSize: off|heightOnly|widthOnly|heightAndWidth|heightAndWidthProportionally, autoSizeReference, useMinimumHeight, minimumHeight, useMinimumWidth, minimumWidth, noLineBreaks}`): the frame fits its text exactly after every edit (typing, pasting, style changes, option changes) in the same undo step (opening a file keeps the frame sizes it gives); it grows and shrinks around the reference point, which stays put in spread space for rotated frames too, never below the minimum height/width and never past 10,000 pt. Width Only and No Line Breaks set each paragraph on one line; Height and Width without No Line Breaks keeps the width; Keep Proportions scales both sides until the text fits. IDML keeps all the options (`AutoSizing…`, `…ForAutoSizing` attributes). Not covered: frames of a thread other than the last, vertical frames, type on a path, and multi-column balancing in Keep Proportions.
 - Balance Columns (Text Frame Options › Balance Columns, `object.textFrameOptions {balanceColumns}`, IDML `VerticalBalanceColumns`): in the frame the story ends in, the columns after the last explicit column break fill to about the same depth (the last may be shorter by a line per column); keep options hold, spanning and split paragraphs keep their own balancing, vertical justification then applies to each column as usual, and vertical frames balance their bands. A frame the text runs on from, or that is overset, fills normally.
-- Text Frame Options dialog, laid out as InDesign's (General, Column Rules, Baseline Options, Auto-Size; framed Columns, Inset Spacing and Vertical Justification groups with spinner fields; Fixed Number shows each column's width as the fields change). Preview shows the edits on the page until OK (one undo step) or Cancel, and values OK would refuse put the page back. Vertical Justification › Paragraph Spacing Limit (`object.textFrameOptions {paragraphSpacingLimit}`, IDML `VerticalThreshold`): with Justify, the extra space goes between paragraphs up to the limit, the rest between lines.
+- Text Frame Options dialog, laid out as InDesign's (General, Column Rules, Baseline Options, Auto-Size; framed Columns, Inset Spacing and Vertical Justification groups with spinner fields; Fixed Number shows each column's width as the fields change). Preview shows the edits on the page until OK (one undo step) or Cancel. An invalid value (such as a gutter that isn't a measure) takes the preview off the page, so the frame shows as it was, and the dialog's status line gives the reason; OK refuses the value too. Preview stays checked and shows the edits again once the value is valid. Vertical Justification › Paragraph Spacing Limit (`object.textFrameOptions {paragraphSpacingLimit}`, IDML `VerticalThreshold`): with Justify, the extra space goes between paragraphs up to the limit, the rest between lines.
 - Place a page of an IDML or DesignCraft document (`file.place {layoutPage}`): its objects, stories, styles and swatches as one group (INDD files are not readable).
 - Articles panel (`article.new/add/remove/options/delete/list`): reading order and content of EPUB and HTML exports.
 - Object ▸ Clipping Path (`object.clippingPath {type: alpha|edges, threshold, tolerance}`): traces the placed image and makes the outline the frame. Clipping paths saved in IDML (Detect Edges, Alpha Channel, Photoshop Path, User-Modified Path; Invert) hide the image outside the path on screen and in PDF and survive IDML export; `object.clippingPathOptions` reports, inverts or removes one (Object ▸ Clipping Path ▸ None).