lxml offers a few different functions to parse strings. Two of them, etree.fromstring() and etree.XML(), seem very similar. The docstring for the former says it's for parsing "strings", while the latter "string constants". Additionally, XML()'s docstring states:
This function can be used to embed "XML literals" in Python code, [...]
What's the functional difference between these functions? When should one be used over the other?