Should we post a general question regarding "why can't I use this macro inside this other macro"?

^^ see title.

I think it should be okay? Compare Should we post a catch-all question answering "What's this font?" on TeX.SX? - TeX - LaTeX Meta Stack Exchange

What's the current problem?

• Answerers keep having to repeat the explanation.
• If they don't, visitors (those who want to learn TeX-programming-language) don't understand what is going on.
• It happens quite frequently (maybe more frequently, this is not easy to search for) – see below.

Meta

• There are 3 types. (if this is made) should they be split into 3 different questions, or only 1?
• What's the duplicate close vote policy?
1. Immediately close questions as duplicate of the corresponding one, unless they (later edit to) mention that they already read the linked question and what exactly they don't understand.

2. Write separate answer that have code to solve OP's specific issue, then link to the corresponding question for the repeated explanation part.

• CW or not? (the font question above isn't CW.)

Example question.

I have a macro \innermacro{...}, when it's used alone it typesets 123 on the document.

Then, I have another macro \outermacro, such that \outermacro{123} results in 456.

Now I try to use \outermacro{\innermacro{...}}, but it raises mysterious errors.

What is going on?

Example existing questions

Generally I think there are 3 types:

1. \innermacro is catcode-changing.

Example:

2. \innermacro is not expandable. ("obviously" this category is the most common)

Example:

Reference:

3. \outermacro does not expand its arguments.

Example:

• Seems like a good idea. Maybe one question with three answers, all CW. Then you can link the appropriate individual answer on a new question. Feb 14 at 13:09
• It's not that \IfSubStr cannot be used in the argument to another macro: it obviously can be. Only \outer tokens or \par cannot appear in the argument to a macro (the latter if the wrapping macro is not \long). Even \verb can appear in an argument, provided it's the last token in the replacement text. Feb 14 at 16:42
• Another question today (I think type 3): tex.stackexchange.com/questions/633891/… Feb 15 at 14:22
• @Marijn (and others) actually I'm somewhat busy now, so someone else can post, otherwise I can do some time later Feb 16 at 7:54
• Type 3, tex.stackexchange.com/questions/643068/… tex.stackexchange.com/questions/642819/… (we're having way too many of those I should really write one soon...) May 5 at 5:52
• May 15 at 4:45