Module:Sandbox/Perryprog/xlink/doc

Background
Eventually I want the loose equivalent of a xsign for all the different special-link-templates I use (I tend to avoid the external link syntax). The end goal is to be able to say something like, and depending on the pattern the URL matches it would emit wikitext (assuming substitution works out well—I wouldn't be surprised if it's impossible) for either diff2, diff4, oldid, and others as time goes on.

Small shorter-term TODO:
 * Actually learn how substitution depth works and all that jazz. (See, which was from substituting the #invoke call.)
 * Given, emit
 * Given, emit
 * Have a less-strict match (e.g., URL param order) for diff-urls with.
 * Switch to diff4 if a numerical value for  is present.
 * And also check if that template or its docs needs fixing, because every time I use it I get the parameters backwards...

Longer-term TODO:
 * A lot.