Xpath - How to select parent based on attribute of child?

How do you select a parent based on the attribute of a child?

I wa开发者_StackOverflownt to select a div:

//*[@id='outer']/div/div/div/div

that has a child with the 'a href' attribute equal to 'www.blah.com':

//*[@id='outer']/div/div/div/div/a[@href='www.blah.com']

The basic fact you need is that predicates can be nested:-

//*[@id='outer']/div/div/div/div[a[@href='www.blah.com']]

//*[@id='outer']/div/div/div/div/a[@href='www.blah.com']/../