Custom Text Reformat

On the Format tab of a field, you will notice that you can select a Text Reformat that will be applied to your field when the user updates the preview.  (Please note - Clicking "Always Reformat" means that the reformat will be applied every time the user updates the preview.  Leaving this setting off means that the field will only be reformatted the first time the user updates the preview.)  If none of the standard text reformat options work for you, then you can set up a custom reformat.  You will see that there are two types - Custom and Custom - digits only.  The Custom - digits only will only reformat numbers.  The Custom will reformat the entire contents of the field.  If you choose either of these options, then a box labeled "Format Mask" will appear.  You can enter your custom format mask in this box.  For example, if you would like a phone number to be formatted as [###] ###-####, then you could enter this in the "Format Mask" field. 

If you set this as a plain custom reformat and checked "Always Reformat" the results would be as follows:
Update one
You entered 123456890
The system applied this format
[###]###-####
The result was [123]456-7890

Update two
Your entry is now [123]456-7890
The system applied this format [###]###-####
The result would be [[12]3]4-56-7890

Update three
Your entry is now
[[12]3]4-56-7890
The system applied this format [###]###-####
The result would be
[[[1]2]3-]4-56-7890


In this case, it would be best to set the reformat to Custom - digits only when using "Always Reformat."  The results would be:
You entered 123456890
The system applied this format
[###]###-#### to ONLY the digits/numbers
The result was [123]456-7890

Update two
Your entry is now [123]456-7890

The system applied this format [###]###-#### to ONLY the digits/numbers
The result was [123]456-7890


Update three
Your entry is now
[123]456-7890
The system applied this format [###]###-#### to ONLY the digits/numbers
The result was [123]456-7890