Just a short stream of keystrokes from Tantek Çelik, 2001 December 20.
IE5.1/Mac is all about three things:
While IE5/Mac was known at release for being smaller and faster than both previous versions and rivals, through some clever improvements in the Tasman engine, noticeable advances have been made both in speed and responsiveness of web pages in IE5.1/Mac.
IE5/Mac broke new ground in W3C standards compliance (CSS1, HTML4, PNG1, ECMA-262, DOM1HTML) for a shipping browser. No other Mac browser yet contains as complete support of these standards as IE5/Mac does (Disagree? Report your standards gripes (er, that should be: well written strictly compliant bug reports) here: email@example.com. Invalid markup and style need not apply.)
IE5.1/Mac continues this steadfast dedication to W3C standards with numerous standards related fixes, mostly minor in nature, but then, when it comes standards, details count. For example, IE5.1/Mac properly supports nondeterministic matching of CSS2 selectors ( child - note the last test: "(this test is harder than the others!).", sibling - note the last test: "This should be maroon"). Try those pages in your current browser for comparison.
During MacHack 2000, a few of the IE/Mac developers decided to add user interface improvements that they wanted for themselves. Turns out others wanted them too!
Tabbing to (or - gasp - clicking) hyperlinks is so passe. Simply type the first few characters of a hyperlink, and watch the focus ring jump to your target. Press 'enter' to load your destination. Leave your mouse in the dust.
Drag any image you want to your Button Bar. Or any hyperlink. Or any hyperlinked image. Exercise for browser tweakers - take a look at your 'toolbar.xml' file and see if you can hack your own active/hover/disabled images for your new buttons as well.
A new preference panel - "Interface Extras" lets you customize some details of IE5.1's user interface. My favorites - open new browser windows when other apps ask IE to go to a page, "flavorize" all your apps, and lust after those cool Gaussian blurred translucent contextual menus .