Help+Manual's variables have several features that make them extremely powerful and flexible:
•You can define variables as HTML variables or as plain-text variables
•You can redefine user variables on a per-topic basis
•You can redefine user variables for your entire project with publishing tasks
HTML variables only insert HTML code in HTML templates and HTML code objects. If you insert an HTML variable in the body of your topic only the text portion of the variable value will be used.
HTML template variables (reference)