{{w}} is a handly little shortcut that equates the following markup:
[[wikipedia:article name]] --> {{w|article name}}
Usage
{{w}} incorporates one kind of pipe trick. As long as the wikipedia article is not disambiguated, then it will automatically get rid of the prepending "wikipedia:". Hence,
{{w|London}}results in London.
However, if the wikipedia title is disambiguated, you must type a little more. For instance,
{{w|London (band)}}renders London (band)- but
{{w|London (band)|London}}renders London
Note for editors from other wikis
Other wikis use something similar to this template. Memory Alpha, for instance uses a template with exactly the same name. However, our {{w}} is a bit different to memoryalpha:template:w, in that it defaults to the name of the page if you don't add your own variable name. In essence, Memory Alpha use {{w}} to do not only what this one does, but also what {{wikipediainfo}} does. The default value of the second variable in this template is the value of first template. That's why :{{w|London}} renders London, because it's actually delivering the following code: [[wikipedia:London|London]] In other iterations of this template around Wikia, it might instead be delivering this code: :<nowiki>W/doc, which is sometimes a very different thing.