Enter/Space do not advance the dialog while a text field has focus, and a
click over another control that stops the mouse (a tool panel drawn over the
dialog area) belongs to that control. DialogBox reads input in _Input, before
the GUI, so both used to advance the dialog as well.
Actions carry the scenario line they were parsed from (SourceLine);
ScenarioParser.SplitLine exposes the parser's line split. ScenarioEvent
remembers its source mod/file and can start at a label. DialogRuntime asks an
optional IDialogDebugger before every action and can be held; DialogBox
resumes a held dialog and aborts one without completing it.