TypeError and use of bold

Hi Cam, 
TypeError is used throughout the spec, but does not link to its definition (particularly how to throw a TypeError). 

Also, the use of bold type faces is inconsistent with other specs: bold in other specs is used to denote a formal definition of something. In WebIDL it is used … kinda at random? :( 

Please use bold type faces where something is defined, otherwise it's really confusing when searching for definitions.