Write maths, see maths is a jQuery plugin for editable areas which gives an instant MathJax preview of the TeX you're writing just above the cursor.
To use it, just call $(selector).writemaths()$ when the page loads.
You can optionally pass in an object with some options:
cleanMaths: a function which does something to the LaTeX before displaying it.callback: a function which is called when the preview is displayed.iFrame: set this to true if you're applying writemaths to something like TinyMCE, which lives inside an iframe.position: the position on the parent element on which to place the preview. It's really the `at option of jquery.ui.position.previewPosition: the position on the preview element to line up with the parent element. It's really the my option of jquery.ui.position.of: the element to position relative to.