A new addition to PowerForms HTML is the ability to sort by multiple columns in a List Query.
Clicking on the Sort with multiple columns presents a text-box which you can use to perform multiple sorting to your list query. As the description says:
Use semicolons (;) to separate column internal names. Sorting is by default ascending. You can add a minus (-) sign at the end of the column name to indicate descending sort.
Example:
Category-;Title
will sort the list query by Category descending and Title ascending.