A tab is never indentation, so flow-collection content reached through a
tab below the continuation indent ('- [' / '\tfoo') is malformed even
though the tab inflates the column. A tab at or past the indent is
separation, and a tab-only blank line stays blank, so both remain valid.
Track a tab in a flow continuation's leading whitespace below the
parent + 1 indent and reject content (but not a closing bracket) reached
through it. Surpasses libyaml on Y79Y/003; whole-suite conformance
400/402, canonical events 308/308.
Mihaela Mihaljevic
98ca76e7af