Redmine

Felix Muster wrote:

I want to use HTML-Code in Redmine.

I have a piece of code that should enable this:

desc “Insert html” + “\n\n” +
” !{{html(html block)}}”
macro :html do |obj, args, text|
text.html_safe
end

but I don't know how to implement...

This is a support request and not a feature request. Please head over to the forums to request help with implementing this custom macro, see e.g. Insert HTML fragments.
Quick test shows the code you've provided isn't working correctly on Redmine trunk.