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[...] list-of-characters


Set strut to cover the maximum height and depths of all the characters specified as argument.


By default, position of page headers (including page numbers) are computed on a per-page basis and the resulting baseline depends on the maximum glyph height of the given header (which extends to the top of the header space). Consequently, the baseline of page headers on successive pages might differ visibly. Presuming, the page numbers are the "limiting factor" here (i.e. are larger than the page header proper) a common baseline can be enforced across all pages by something like

\setuppagenumbering[location={header,margin}, style=\bfc\setcharstrut{0123456789}\strut, strut=no]

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