In the examples under UI gallery I checked the design time configuration, where in I see manytimes for the property they are selecting something like this "Declare_UIGalleryControls.pyTextArea1".What kind of property is this.where it is declared I am not getting.
But when I check in app explorer I dont see this property defined at all.
You can find the UI Gallery and all the examples by choosing from the Designer Studio link in the top left corner, selecting User Interface > UI Gallery.
From here you can choose any sample or component and see all the different configurations. For example this is the Autocomplete component:
By clicking the View Design-Time Configuration link you will be presented with the rule that was used to create the UI Gallery sample. From here you can reverse engineer the component and in some cases copy and past the objects right into your rules.