Add spanning (multi-row) column headers to tfl_table#43
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`tfl_table(col_header_sep = "|||")` (default on; a single NA disables) splits each column label into stacked, bottom-aligned header rows and auto-merges adjacent equal cells into spanning headers. A spanner's width is the sum of the columns beneath it, and a spanned block is atomic across column-continuation pages (an over-wide block routes to overflow_action). When no label contains the separator the header is a single row and output is byte-identical to before (R == 1 short-circuit). Span detection (.compute_header_spans) uses a hierarchical closed-boundary algorithm: merges happen only within a shared parent span, empty cells are transparent singletons, and the row-header/data divide is a hard boundary. Merge comparison uses raw text while display right-trims, so a trailing space prevents an unwanted merge. Width is handled by measuring only each column's leaf segment, then distributing each spanner's deficit across its member columns (.apply_header_span_widths) on both the natural and minimum width vectors; the existing water-fill / pagination / reconcile machinery then runs unchanged. paginate_cols packs by atoms so spans never split. Also fixed wrap auto-detection to key off the leaf segment (a super-header's spaces must not make a leaf column wrap-eligible). The row/column span logic shares a .span_deficit() kernel. Adds col_header_span_rule (default TRUE): each multi-column spanner is underlined, with adjacent groups' rules separated by a gap equal to the cell's horizontal padding; styled via gp$col_header_span_rule (falls back to gp$col_header_rule). Tests in test-span_header.R cover the algorithm, slicing, validation, spanner x-extent (= sum of member columns), atomic pagination, over-wide error, underline gap/toggle, and the R == 1 regression lock. Adds a "Spanning column headers" vignette section; updates design docs (D-53). Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
The new spanning-header chunks used fig.height = 4, which leaves a content area (~2.55 in) below the default min_content_height (3 in), so export_tfl() aborted during vignette re-building and failed R CMD check on every CI job (and pkgdown). Use fig.height = 8.5 to match the other table chunks in this vignette, giving ample content height. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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tfl_table(col_header_sep = "|||")(default on; a single NA disables) splits each column label into stacked, bottom-aligned header rows and auto-merges adjacent equal cells into spanning headers. A spanner's width is the sum of the columns beneath it, and a spanned block is atomic across column-continuation pages (an over-wide block routes to overflow_action). When no label contains the separator the header is a single row and output is byte-identical to before (R == 1 short-circuit).Span detection (.compute_header_spans) uses a hierarchical closed-boundary algorithm: merges happen only within a shared parent span, empty cells are transparent singletons, and the row-header/data divide is a hard boundary. Merge comparison uses raw text while display right-trims, so a trailing space prevents an unwanted merge.
Width is handled by measuring only each column's leaf segment, then distributing each spanner's deficit across its member columns (.apply_header_span_widths) on both the natural and minimum width vectors; the existing water-fill / pagination / reconcile machinery then runs unchanged. paginate_cols packs by atoms so spans never split. Also fixed wrap auto-detection to key off the leaf segment (a super-header's spaces must not make a leaf column wrap-eligible). The row/column span logic shares a .span_deficit() kernel.
Adds col_header_span_rule (default TRUE): each multi-column spanner is underlined, with adjacent groups' rules separated by a gap equal to the cell's horizontal padding; styled via gp$col_header_span_rule (falls back to gp$col_header_rule).
Tests in test-span_header.R cover the algorithm, slicing, validation, spanner x-extent (= sum of member columns), atomic pagination, over-wide error, underline gap/toggle, and the R == 1 regression lock. Adds a "Spanning column headers" vignette section; updates design docs (D-53).