Matching begin and end tags

[johmara]

Describe the need of your request

At the moment the begin and end tags have no requirement by the lexer to match. In order to prevent mistakes by the user to miss a matching end or begin tag this needs to be fixed.

Proposed solution

Change the bnf and flex files to make the begin and end tags matching.

Alternatives you've considered

No response

Additional context

There is complexity here as the language is injected and the matches need to be able to resolve in an injected context.