What is "[+]" in xemacs regular expression?

Question

In (my) XEmacs 21.4, describe-variable for gdb-prompt-pattern gives:

Value: "^>\\|^(.*gdb[+]?) *\\|^---Type <return> to.*--- *"

What is the "[+]" in there? Does it just mean "the + character"? If so, why not use "\+"?

Answer 1

in regular expression [+] is symbol +

any symbol in [] is symbol except -

Answer 2

In your context, [+] is the same as \+, that is matching the + character, and I imagine the original writer of that regexp either did so for readability reasons, or perhaps because [+] used to be in the past some set of chars like [-+]