Marijn, please confirm if I understand correctly.

Lezer has the ability to avoid some token - ![/] …
but it can be only one sign ( because it is regexp ), for string, we cant use !’//’ or some similar.
So we can`t write to prohibit something specific, we can only write clear rules, and after, with the helping of snippets we can describe expectations and errors? Am I right?

And , i am trying to find it, but maybe you keep my time - can we get a length of the current history ( undo / redo ), if i want to know - something is changed after initial inside codeMirror 6

![...] syntax doesn’t really prohibit anything, it just matches any character not in that set, rather like JS regexp’s [^...] notation.

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okay, but can we avoid two characters? as [^…]{2,2}

Give the character set a name and use that name twice in a row.

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