# What is “dimen” in the documentation for the ifthen package?

In the documentation for the `ifthen` package, there is a test called `\lengthtest` which compares two `<dimen>` parameters with the operators `<`, `>` or `=`. (For other test commands, `<dimen>` is usually `<string>` or `<number>`.) Searching for "dimen" in the document and on google, I find nothing to explain what it means.

What is `<dimen>`?

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AFAIK, this would be referring to a length, so, either 1pt, 2cm, 5mm, 10em, etc. or previously defined lengths: \textwidth, \parskip, 4\itemsep, etc.

This would come in handy, for example, if you want to do one thing if the length of your title is larger than the width of the page, and a different thing if it is smaller than it...

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 Makes sense, now that you say it... – Tomas Lycken Nov 2 '10 at 23:21 DEK originally used ; Leslie Lamport changed the name to . – Matthew Leingang Nov 3 '10 at 9:44 `\parskip` and `\itemsep` are both skips, not dimensions. – TH. May 15 '11 at 0:51

Quoting from Donald E. Knuth, The TeXbook, pages 59, 61:

Henceforth we shall use the term `<dimen>` to stand for a legitimate TeX dimension. [...] [A] complete definition of everything that a `<dimen>` can be will be given in Chapter 24.

My (hopefully educated) guess is that this is what the `ifthen` documentation refers to.

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