Parses str which is marked up with the Pango text markup language, setting the label’s text and attribute list
based on the parse results.
If characters in str are preceded by an underscore, they are underlined indicating that they represent a keyboard
accelerator called a mnemonic.
The mnemonic key can be used to activate another widget, chosen automatically, or explicitly using set_mnemonic_widget.
| this |
a Label |
| str |
a markup string (see Pango markup format) |