html element id as javascript variable

Question

Consider the following code:

Answer 1

First off, how long has this "feature" been around?

It is a Microsoft-ism that cropped up around IE 4 if I remember correctly.

Some other browsers have added support for it in an effort to be compatible with badly written code that depends on it. Some may only support it in quirks mode.

this doesn't seem like a very good "feature" to have

Correct. Don't use it. :)