BobRay,
this is exactly what I was looking for,
thank you very much!
I could have found it in the MODx-Revolution-documentation,
chapter "Snippets".
I have to additions:
1) In Revolution-syntax one has to use 2 brackets instead of one :
[[!code? &content=
`<p>blabla</p>`
]]
2) If you use singlequotes or no quotes, it works for every html-code, but not for php-code or html-code that uses quotes. you have to use backticks as in the example above, then it works like a charm.
(my case closed)