This function can be used to determine if there are any fonts
available to render all characters in a certain string, or when
used in combination with pango.types.AttrType.Fallback, to check if a
certain font supports all the characters in the string.
Counts the number of unknown glyphs in layout.
This function can be used to determine if there are any fonts available to render all characters in a certain string, or when used in combination with pango.types.AttrType.Fallback, to check if a certain font supports all the characters in the string.