Editorial style checker

This is a pattern check, not a proofreader. It catches what a rule can catch: spelling pairs from a fixed table, date and number formats, the comma before and, heading case on Markdown headings and short standalone lines, and the words you list. Meaning-dependent pairs like licence and license are flagged for you, never swapped, because the right word depends on sense. Plain-text headings without a # mark are only guessed when they sit alone between blank lines. The GOV.UK preset covers the machine-checkable slice of that guide, not the whole of it.