Unlike strings and arrays, regular expressions are not anchored at the current position of the cursor when used in ve.ui.Sequence, i.e. while a sequence constructed from 'foo' only triggers when foo is directly before the cursor, a sequence from /foo/ will trigger whenever the string foo is anywhere before the cursor.
This is a bit unexpected, so the documentation should advice to use a $ in the RegExp to anchor it to the cursor and thus make it behave like strings and arrays.