How to validate??

[CoraLover]

Hi, i need to validate the following:

For instance, i've this value: "You;Can;Do;It;" entered in a textfield.
How can i validate that the ";" is entered after every word? If 1 ";" is missing, i've to alert the user...

[x_goose_x]

<input type="text" onchange="if ( 0 <= this.value.indexOf(' ') ) { alert('You forgot a semi-colon') };">