[Zope] basic &dtml syntax question

[Jason Cunliffe]

example: <img src="&dtml-absolute_url;">
                                     ^
                                     ^
                                     ^
                                     ?

Please can anyone explain why <&dtml...> syntax has a semi-colon ; at the
end?

What is for?
Why is necessary? etc
How to use/abuse it?

thanks

>>> Jason