"single line" format ?

[kapouer]

This is very naive proposal but it makes sense for me, so why not for the spec...
format: singleline
pattern: /^[^\n\r]*$/

The idea is to be able to tell when a string is supposed to not be a multiline string.

[gregsdennis]

I see you have a regex there to qualify when a string is a single line. It's pretty simple, too.

Typically, formats have been for things that either can't be perfectly qualified by regex or are really complicated, like URIs.

Also, I wonder if the utility of this warrants a new format. Seems like maybe it would be better to include it in a listing of "common" expressions that can be used with the pattern keyword.

[handrews]

This should just be done with pattern, and if you want to name it, you can make a definition under definitions (current) or $defs (future). format is for things that have semantic meaning that isn't apparent from a regex (how many of us would recognize an email address regex if we saw one? they're absurdly complex if they're even useful at all).