Using inheritance
Themes can inherit properties from a parent theme.
Using theme inheritance
A theme can inherit from another theme by specifying the parent theme in the extends attribute of the root tag:
<theme extends='MyOtherTheme'>
In that case, the new theme will inherit all the properties from its parent. In the previous code example, the new theme inherits all of the properties of the parent theme, MyOtherTheme.
The property definitions in the new "child" theme are merged with those of the "parent" theme. Any existing properties from the parent theme are preserved and therefore take precedence over the ones defined in the child theme unless explicitly cited as overridden. Parent properties are overridden by specifying the override attribute:
<control override='true'>