Decreases the left indent of all paragraphs contained in the current text selection. If no text is selected, this method decreases the left indent at the text input position. Left indent positions are defined through the paragraphs' tab positions and the indents of the paragraphs in front and behind the paragraph with the text input position.
The return value is True, if at least one indent could be changed. It is False, if the minimum value has been reached.