Add a comment with what this function does and returns and rename it to textblock_is_task.

It should receive a textblock if you place it in this file, not a security descriptor and I think it's better that it return the task's id, so it doesn't make the query for the task unless you really have too. You should also replace the regexp in common/security.php with this function (it appears two times there I think).

This is left over from the copied code from common/security. This should have been return false.

Add a link to edit the task's tags while you are at it.

Here you do need the require_once

Change this to use textblock_is_task also.

A more friendly comment :P 
If textblock security descriptor is a task, returns the task's id, otherwise return false.

Either call it textblock_security_is_task or pass a textblock, not a security descriptor.

No need for require_once here.

Our coding style enforces maximum 80 characters per line, so put the enter back here :)

Remove this empty line.

textblock_security_is_task

We should call it "Editeaza enunt" for tasks.