(?=^((?!the text that should not be present).)+$)(^the text that should be present$)
Here is a Javascript snippet to check that a string does not contain two dashes (–) directly following each other:
var regex = /(?=^((?!--).)+$)(^[a-z\-]{1,10}$)/; true === regex.test('abc-def'); true === regex.test('-abc-def-'); false === regex.test('abc--def'); false === regex.test('abc---def');