Formating or creatin a custom fields" with specific format

[slhuilli]

Hello everybody,

I have a problem and I don't find any tutorial for developping that... (I am a programmer)
I need to save/use a custom field (in Joomla3 only, not4 for the moment) with a specific format (as the SLRN format of Slave Regster on the net).
I want to have a custom fields (not only a simple text formated on the render but a masked field when I write ther numbers) with the format as xxx-xxx-xxx when the user (me !) will write this "number" (in fact, it is not a number but a string)
I want to have a masked input text type when I write the number in the administrator part (no user will write that, only me, the admin of the site)

Where can I find an example to adapt for my use, a tutorial which explain how do that ?

Thanks