pub fn headline(error: &Error) -> StringExpand description
What a caller reads when clap refuses a command line.
clap renders a refusal as the message, then a usage block, then a line
telling the caller to try --help. Two of those three are the grammar and a
pointer to it, and #306
already settled what this binary does with both: a refusal names where the
grammar is rather than reprinting it, and the pointer names the binary so a
caller can paste it. So the message is what is taken here, with any tip:
line under it, and fail supplies the prefix and the pointer.
The message text is clap’s, which is the whole reason for taking the
crate: it names the offending word, and it enumerates the legal values of a
flag that has a closed set.