css - IE5.5 Filters - why is filter: gradient(properties) not available, while filter: alpha(properties) is? -

here's question experts out there.

when ie5.5 launched, came range of new filters, such as:

filter:progid:dximagetransform.microsoft.gradient(sproperties). 

later versions of ie supports shorter method enabling alpha-transparency:

filter: alpha(opacity = 50); 

does have explanation, why ie doesn't support shorter method gradient, e.g. filter: gradient(startcolor, endcolor)?

the whole filter style proprietary microsoft , ie, , has never been subject kind of external standardisation process.

therefore choice of syntax , supported or not entirely down whims of microsoft.

one thing worth knowing filter:progid:.... syntax is invalid css, due colon after progid. have seen cases syntax has caused serious parsing errors in other browsers. (in 1 case, firefox 3.6 refused parse further down stylesheet after encountering rotation filter)

this sort of issue may possibly have been part of motivation providing shorter alternative syntaxes, since @ least syntactically valid css, although doesn't explain why have done filters , not of them.

other that, there's no reason know of why have chosen provide short-cut variants of of filter style , not others. perhaps decided ones in popular use? whatever reasons decisions made, these short styles apply ie6 , ie7, , they're in distant past , of historic interest now.

with ie8, replaced filter -ms-filter, , went longhand versions of styles, , added requirement wrap value in quotes (thus resolving invalid css issue described above).

with ie9, whole question becomes moot, because they've dropped filter style entirely, , implemented standard css3 alternatives.

if you're trying work filter styles, gradients, recommend looking tools such css3pie, javascript wrapper designed allow ie6-8 support css3 standard styles gradients, etc. allows write css code without having use non-standard ie-only filters. other similar tools exist other filter styles.