Which characters are illegal within a branch name?

Question

The title says it all...

Answer 1

Google says:

A branch name can not:
    - Have a path component that begins with "."
    - Have a double dot ".."
    - Have an ASCII control character, "~", "^", ":" or SP, anywhere
    - End with a "/"
    - End with ".lock"
    - Contain a "\" (backslash

Update

Thanks @Jakub Narębski. The man page for git check-ref-format has more details.