A Property Set is a collection of properties and classes that are applied to a Control when that Control is linked to that Property Set. Almost every type of Control can have one or more Property Sets defined in a Presentation Template.
One Property Set for each Control type can be marked as its default. When a Control of that type is dragged onto a Page it is automatically linked to the default Property Set.
Changes to a Property Set affect all Controls that are linked to it. For example, adding a CSS class to a Property Set will automatically add that class to every Control that is linked to it.
Themes downloaded from the Resource Hub have a collection of pre-defined Property Sets covering the styling options available in that Theme. For example, Themes based on the Bootstrap framework have Property Sets defined for primary and secondary colours for every appropriate type of Control.
When a Form is configured to use a Theme, all the Property Sets defined in the Theme’s Presentation Template are available to Controls added to that Form.
The current Property Set of a Control can be seen in the Control’s Properties View.
The Control can be linked to another Property Set by clicking on the 
icon and selecting Link to Property Set.
This opens a dialog previewing all Property Sets available for that Control Type. Pressing OK will link the Control to the selected Property Set.
