[NTG-context] checking whether file is landscape or portrait

[Arthur Reutenauer]

On Tue, Jan 28, 2020 at 05:43:36PM +0100, Pablo Rodriguez wrote:
> I’m afraid this is the second time I’m aware of the existence of \ifdim
> (the first time was when reading previous message from Taco 😅).

  It’s a TeX primitive.  From the TeXbook, chapter 20:

	* \ifdim<dimen1><relation><dimen2>  (compares two dimensions)
	This is like \ifnum, but it compares two <dimen> values.  For
	example, to test whether the value of \hsize exceeds 100pt, you
	can say	‘\ifdim\hsize>100pt’.

  The definition of \ifnum, right above it, states:

	* \ifnum<number1><relation><number2>  (compares two integers)
	The <relation> must be either ‘<’ or ‘=’ or ‘>’.  The two
	integer numbers are compared to each other in the usual way, and
	the result is true or false accordingly.

  Best,

		Arthur