<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def from_tag(cls, tag, schemas, ext='.rnc'):
 """load a schema using an element's tag. schemas can be a string or a list of strings"""

        return cls(fn=cls.filename(tag, schemas, ext=ext))