mjhjmtu

I was curious and found the following definition for the macro textcolor defined in the package xcolor:

deftextcolor#1#@textcolor#1
def@textcolor#1#2#3protectleavevmodecolor#1#2#3

However, I use the macro with only two arguments and not three arguments:

textcolorbluefoo

What I don't understand for this definition is:

1. What is the meaning of the syntax textcolor#1#?


2. What will be the third argument the macro @textcolor will get in the example above?

This is primitive tex syntax that really shouldn't be used in a latex package. It's used here as in 1993 fitting this all into a 640K machine we were really short of space and saving a few dozen bytes by shortcutting the definition was worth it.

If you go

deffoo#1#zzz #1 zzz

then #1 is everything from foo to the first brace, so

foo one two three zzz

then #1 would be one two three

Using this allows textcolor to grab any optional arguments without actually parsing for them and then re-insert them so color sees them.

so compare

textcolorbluefoo

and

textcolor[rgb]0,0,1foo

in the first case #1 is empty so the expansion is

 @textcolorbluefoo

which is

 protectleavevmodecolorbluefoo

but in the second case #1 is [rgb] (including the brackets) so the first expansion is

@textcolor[rgb]0,0,1foo

which is

 protectleavevmodecolor[rgb]0,0,1foo

so the [rgb] isn't really ever seen by textcolor as an optional argument, it is just grabbed and passed to color.