Including a literal '[' in SIP message is difficult

[rkday]

It would be nice to be able to treat '[' as a literal [ character, rather than as the start of a keyword or variable.

[rkday]

(It's possible to insert it by using \x5B to insert the corresponding ASCII byte.)

[wdoekes]

Or [openbracket] and [closebracket].

[wdoekes]

IMO, this is better fixed with documentation than with extra code.