Function parse_shorter_head_reading 

pub fn parse_shorter_head_reading(
    working_set: &mut StateWorkingSet<'_>,
    head: Span,
    input_type: Option<&Type>,
) -> Option<Expression>

Re-parse a command head that greedily matched a multi-word subcommand as its next shorter reading, demoting the trailing words to arguments over the real buffer spans.

head must be resolvable in working_set; returns None for single-word heads.