pub fn opening_directive(trimmed: &str) -> Option<(usize, String, String)>Expand description
If the line is an opening directive (::name[attrs]), return (depth, name, attrs_str).
Tolerates spaces/tabs between the colons and the block name (:: hero[...])
— a common generated-markup slip that previously leaked the whole directive
line into rendered output as literal text. Callers that do offset math on
the line must use [directive_name_start] rather than assuming the name
begins at depth.