A single quote is actually shorthand for the quote special form

  'foo
  (quote foo)
  '(1 2 3)
  (quote (1 2 3))

It basically does not evaluate its arguments but returns whatever it is. So instead of the value of foo, it the symbol foo. The list example does not evaluate it either, it would normally try to apply the first element as a function, but instead we get the list of numbers.

This is just Scheme. It's nothing to do with SXML.

#:foo is a keyword argument and '(apache httpd) is a quoted list containing the symbols apache and httpd.

Angled brackets have no special meaning, they are just part of the identifier.

While I don't write Scheme, I believe it is Scheme -- one of the goals of the GNU project is to have every GNU tool be configurable with Scheme (which is why GNU has a Scheme implementation as opposed to a Common LISP implementation).

Not only does GNU have a Common Lisp implementation, in fact there are two:

GCL: https://www.gnu.org/software/gcl/

CLISP: http://clisp.org/

I've installed CLISP before, why didn't I know it was a GNU project? Fair enough, I stand corrected. :D

Well, they have GCL and CLisp too!