When gathering project requirements, hearing a client ask for "WYSIWYG" can be cause for concern. Clients see an easy way to manage content but are often unaware of potential consequences. As more tools are leveraged within an editor, the potential that something may clash with CSS on output can increase. Prudent developers may immediately work to limit the set of tools provided to the client. If you're lucky, you can get away with supporting "links", "bold", "italics", but not "underline"!