Main private entry point for building composite components from template XML.
Most likely you do not need to call this function in applications as templates are handled by `GtkWidget`.
this |
a `GtkBuilder` |
object |
the object that is being extended |
template_type |
the type that the template is for |
buffer |
the string to parse |
length |
the length of |
A positive value on success, 0 if an error occurred |