[kazinator]

Since you control the \\d format, why would you allow/support anything but a space as a separator? That's just to distinguish it from a comment like "\\delete empty nodes" that is not the \\d debug notation.

If tabs are supported,

  [ \t]

is still shorter than

  [[:space:]]

and if we include all the "isspace" characters from ASCII (vertical tab, form feed, embedded carriage return) except for the line feed that would never occur due to separating lines, we just break even on pure character count:

  [_\t\v\f\r]

TVFR all fall under the left hand, backspace under the right, and nothing requires Shift.

The resulting character class does exactly the same thing under any locale.

[nerdponx]

There's also [:blank:], which is just space and tab. Both I think are perfectly readable and reasonable options that communicate intent nicely.

[kazinator]

ISO C99 says, of the isblank function (to which [:blank:] is related:

The isblank function tests for any character that is a standard blank character or is one of a locale-specific set of characters for which isspace is true and that is used to separate words within a line of text. The standard blank characters are the following: space (’ ’), and horizontal tab (’\t’). In the "C" locale, isblank returns true only for the standard blank characters.

[:blank:] is only the same thing as [\t ] (tab space) if you run your scripts and Awk and everything in the "C" locale.

[nerdponx]

Interesting, the GNU Grep manual describes both character classes as behaving as if you are in the C locale. I shouldn't have assumed it was the same as in the C standard!