| Element | Value | |
| m.size() | 1 + e.mark_count() | |
| m.empty() | false | |
| m.prefix().first | first | |
| m.prefix().second | first | |
| m.prefix().matched | false | |
| m.suffix().first | last | |
| m.suffix().second | last | |
| m.suffix().matched | false | |
| m[0].first | first | |
| m[0].second | last | |
| m[0].matched | true | |
| m[n].first | ||
| m[n].second | ||
| m[n].matched | For all integers 0 < n < m.size(), true if sub-expression n participated in
the match, false otherwise. |