Creating regex using automata

Keyword: GNFA.

You can use automata diagrams to make creating regex easier.

• states with transitions labelled by regex
• some states accept regex, some reject
• if multiple final states, create new final state, with epsilon (free) transitions from old final states
• if multiple arrows from initial state, create new initial state with epsilon transition to old initial state
• rip out states by combining arrow labels using union (or), until you only have first and last states left

Example: I want to match unclosed input elements, like <input type="checkbox">

Diagrams showing how to build it: