TrvActionFontBold is the action for "Bold" command.
TrvActionFontBold = class(TrvActionFontStyle)
This action does not introduce any new properties in addition to properties of TrvAction.
This action makes the selected text bold (or not bold if already bold). It adds/removes fsBold in Style property for styles of all selected text items.
This is a checkbox-like action, its Checked property is updated depending on the state of selection (or the current text style).