Get HTML Source of WebElement in Selenium WebDriver using Python

I'm using the Python bindings to run Selenium WebDriver.

from selenium import webdriver
wd = webdriver.Firefox()

I know I can grab a webelement like so...

elem = wd.find_element_by_css_selector('#my-id')

And I know I can get the full page source with...

wd.page_source

But is there anyway to get the "element source"?

elem.source   # <-- returns the HTML as a string

The selenium webdriver docs for Python are basically non-existent and I don't see anything in the code that seems to enable that functionality.

Any thoughts on the best way to access the HTML of an element (and its children)?