to allow underscore change regex to ^[a-z,A-Z][[:alnum:]]*$ in Question.php and form-control to ^[a-zA-Z][a-zA-Z0-9]*$

This break all Expression Manager, already explain a lot what this change was made.

okey, did not know, it was included in <2.06 but then suddenly changed

tabs.php would be the form controll pattern to change to ^[a-zA-Z][a-zA-Z0-9]*$

denis, where do the EM break with these changes? couldn't trigger that.. i mean, underscore is allowed when importing questions, there's an exception for 'archiveimport'

Question code : QCODE, sub question code : SQ
=> EM see QCODE_SQ

We disallow same question code for this reason in Question::model

There are other reason too, a lot of bug closed.

Ah, thanks for clarification!