The reference to entity “foo” must end with the ‘;’ delimiter

The ampersand & is a special character in HTML and XML. If you want to use it as a normal character, you have to encode it correctly. Write & instead of &:

src="https://stackoverflow.com/questions/6483807/...9623&w=180&h=46&style=white&variant=text&loc=en_US"

& denotes the start of an encoded entity, such as < for <, or & for &. In your case the parser tries to interpret &w as an entity. But entities are always terminated by an ;, thus if the ; is missing you get the error message.