In law, must and shall are important words. Must and shall indicate that an action is required, it has to happen, it is a part of the process, proceeding, or hearing that can’t be ignored. Contrast that with “may”, which implies that it doesn’t matter if the thing happens or not.
One thing that is supposed to happen in a criminal case, is that the Judge must inform the defendant about the range of punishment before he pleads guilty. That is, the defendant must know how much time he’s look at before he says “I’m guilty”. Here is the shall if you want to read it-
Texas Code of Criminal Procedure 26.13