Use [u= rl] when certain characters would trip up the code. Remember it because you'= ll need
[url] to fix spaces in urls. But anywhere a &, $, !, space, etc c= ould be a problem: commonly, all search/append/replace/delete tags (&), s= howif/hideif (!), urls. Note that you don't have to waste your time url'ing e= very damn value written to a db. If you control the value and know it's clea= n, like a T or F or a number or word from a value list, no need. When a user= inputs or you pull something like company names from a db, that's when you n= eed it.
[input] is used when quote marks and returns will trip things= up. Values within <input> tags and in java scripts. Not just in <t= ext area> but also in all other <input> tags, i.e., value=3D"[input= ][whatever][/input]" -- same idea about js.
[conver= tchars] to make things right again when you display text on your page.