Force insert value to TextBox in a certain order

[ISMAILC]

Hi, I need help please.

I have a textbox with char length 30 & a tooltip providing user information on how the value should look like.

The value should be in the following order of: Test1 Test2 Test3
but the user's keep on getting it wrong: Test1 Test3 Test2
all kinds of order even though they have been educated via mail & tooltip.

In the past I had 3 different text boxes that adds up to one and was cancelled as the users got confused. The values are string & can be anything, it's just the order of the value is incorrect to make the field valid.

I have a backround image on textbox indicating the format

Any Ideas?

Regards