The text that takes the place of the span the fix covers, which is what carrying it out amounts to. Every kind of fix is named here, so a new one cannot quietly inherit the behaviour of another.
Whether the fix names a span that can be changed at all. A rule that cannot locate its finding falls back to SourceLocation.invalid, and carrying that out would cut somewhere else entirely. An insertion is a span of no width, written with its end one column before its start, so only the lines have to be real.
Readonlyname: "LintQuickFix"
Helper for working with quick fixes.