With mobile web design there is a growing trend of hiding content and hinting to the user it is there and letting them choose when they wish to access it.

traditionall hidden content was not use because it wasn’t semantic and could make finding information on the website difficult.

But by using Javascript to change classes in the markup, classes that relate to CSS that make the content visible. Often coupled with a sliding animation creates the impression of space beyond the screen and as this technique becomes more popular users will except it as common knowledge. Justifying its use.

The Facebook mobile app presents users with a symbol containing three horizontal lines that they can click to display the side bar.

This three line symbol appears on a number of apps to represent a hidden menu showing a trend towards creating a new standard.