Pros:
* Ignored as a comment in other browsers – it’s only run by Windows IE.
* Works with (X)HTML Strict & Transitional Doctypes
* Does not break W3C validation
* Lightweight and very easily deployed
* Works with existing in-line or external CSS rules based on class or ID selectors
* Works with old-style img align=”left” or align=”right” attributes
* Runs after any existing Body Onload code
* Works with imagemaps and input images using a special version
Cons:
* Doesn’t work in IE versions earlier than 5.5 – the AlphaImageLoader filter wasn’t introduced until version 5.5. There is no cure for earlier versions.
* Requires JavaScript to be enabled – the estimations for how many people choose not to use JS vary wildly. See note [1]
* CSS backround PNGs not supported – experimentation revealed I could traverse the Stylesheets collection and use the AlphaImageLoader trick to replace all background-image attributes containing PNGs, but then background-repeat would not work, and anchors placed over non-transparent parts of the image were not clickable 🙁
* CSS rules for the PNG images based on the img selector are lost, but this is easily rectified by adding a class selector to your img rule such that img{..} becomes img,.png{..} – then add the attribute class=”png” to each of your PNGs.