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When using e.g. the [12pt] option for a document class like


what does (Xe)LaTeX actually do/set?

I noticed that for example a multicols environment behaves different whether I use the [12pt], or no such option but a \fontsize{12pt}{14.5pt}\selectfont at the beginning of the document, with some spaces around headlines being 1 or 2 pt different. (The value of 14.5pt I got from \the\baselineskip from the original [12pt] version).

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up vote 10 down vote accepted

There are two major points here:

  1. the option loads the file size12.clo which sets the lengths and sizes (not just the sizes for \small etc., but also paragraph indentation, the skip amount, apparently, a default for the margins, etc.

  2. a package can assume font sizes are set that way by convention and look at the global options to make some changes in its own setup.

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some document classes (for example amsart and siblings) have the size option code built into the .cls file. however, i know of no latex document class that departs from the basic model of \normalsize, \large, \small, etc., within the provided range of sizes. (the provided sizes of the ams classes are a superset of the sizes in the basic classes, adding \Small and \SMALL.) – barbara beeton Jan 18 '13 at 13:44

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