Just stumbled upon this in a borrowed css file - something I've never noticed before, and punctuation in context is inherently hard to google:
.ez-radio { zoom: 1; *display:inline; _height:15px; }
What's the '*' prefix do?
And for the matter the underscore in _height?
Is this some new CSS3 trickery?
It's used for CSS hacks in Internet Explorer.
* is IE 6 - 7 only (thank you, mck89!)
_ is IE 6 and below.
Don't use them. If you need browser specific CSS definitions, use specialized CSS definitions instead.
Those symbols are used to target IE lower version browsers called it CSS HACKS.
FF, Chrome or Safari always ignored those strings in CSS class.
dont want to duplicate Zanathel's answer, but its important to mention:
please do not use them in your stylesheet, keep it hack-free
when you need to use hacks, dont use hacks, use conditional comments, and place your ie specific css in these files
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CSS reset - purpose of asterik within a style
I was reading through the CSS styles for HTML5BoilerPlate, and I came across this unfamiliar line:
button, input, select, textarea {
font-size: 100%; margin: 0; vertical-align: baseline; *vertical-align: middle;
}
In particular, the second ****vertical-align***, why call twice and put an asterisk in front of it.
If anyone knows the name of the technique or why it's used, it would be a great help
Thanks!
-Adrian
It's a nasty hack that can be used to target older versions of IE (other browsers ignore the invalid asterisk-prefixed value). Definitely not a good idea, far better to use IE conditional stylesheets or similar techniques.
It's a CSS hack for Internet Explorer browsers:
*property: value
If you add a non-alphanumeric character such as an asterisk (*) immediately before a property name, the property will be applied in IE and not in other browsers. Unlike with the hyphen and underscore method, the CSS specification makes no reservations for the asterisk as a prefix, so use of this hack could result in unexpected behavior as the CSS specifications evolve.
property: value applies the property value in IE 7 and below. It may or may not work in future versions. Warning: this uses invalid CSS.
from here
This is a css hack and used to target IE7 browser.
For more reference see How to Target IE6, IE7, and IE8 Uniquely with 4 Characters
It's an IE6 hack. If you put the * in front of a CSS attribute, it will only be read by IE6. Since IE6 usage is now down to 1% of the world, we can forget about this hack (unless you live in China)
As I'm sure you all know, Internet Explorer can handle simple gradients. Here is a snippet from Twitter Bootstrap, for example:
filter: progid:DXImageTransform.Microsoft.gradient(startColorstr='#ffffff', endColorstr='#e6e6e6', GradientType=0);
However, I've seen some people use two CSS rules (one for IE < 8 and one for IE 8), like so:
filter:progid:DXImageTransform.Microsoft.gradient(GradientType=0, startColorstr='#7fbf4d', endColorstr='#63a62f'); /* For Internet Explorer 5.5 - 7 */
-ms-filter: "progid:DXImageTransform.Microsoft.gradient(GradientType=0, startColorstr='#7fbf4d', endColorstr='#63a62f')"; /* For Internet Explorer 8 */
My question is, is the second rule really necessary? Twitter Bootstrap is quite thorough, yet it doesn't use any "-ms-filter" rules. According to this page, the -ms-filter attribute is an extension to CSS, and can be used as a synonym for filter in IE8 Standards mode.
My suggestion:
Use CSS3Pie -- http://css3pie.com/
This is a JavaScript library for IE6, IE7 and IE8 that patches in support for several CSS3 features, including gradients.
Yes, you can use the horrible IE-specific filter styles if you want, but CSS3Pie allows you to use standard CSS styles for these features. Much easier.
To actually answer your direct question:
Yes, the -ms-filter style is usually required. IE8 will always us it instead of filter, which is used primarily for IE6 and IE7. In some cases filter will work in IE8, but not all, so it's best to use -ms-filter to ensure IE8 compatibility.
[EDITED]
Why did they change it? Because when they released IE8, Microsoft made a big point of trying to be "standards compliant".
For a browser to be standard-compliant, it should use a vendor prefix for any CSS property it supports that is not a finalized W3C standard. So by adding the -ms- prefix, Microsoft were trying to (belatedly) undo their pollution of the global CSS namespace.
In addition, the quotes were added, because the old filter syntax without the quotes was invalid CSS (mainly because of the colon after progid), and caused issues with some browsers. (I had an instance some time ago with Firefox 3.6 where it was dropping all styles following a filter style that rotated an element - took ages to work out what was happening).
The fact that Microsoft retained backward compatibility with the original filter syntax, was largely a matter of pragmatism. MS couldn't afford to break all the sites using the old syntax. But there was a strong implication from Microsoft that developers should use both because they would drop support for the old filter style in subsequent versions of IE. As it turned out, they dropped support for both filter and -ms-filer in one fell swoop, but the implications given at the release of IE8 were sufficient for it to become recommended practice to provide both syntaxes in your stylesheet.
At the time when IE8 was released, XHTML was the new flavor of the month, and writing code that validated perfectly was top of the list for a lot of developers. This was probably a strong driving force in the change of syntax to include the quotes. Because of the stray colons, it is impossible to write CSS that validates using the old filter style. Using the new -ms-filter styles instead allowed people to write valid CSS. As good ideas go, this one didn't really work out because of course people had to keep using the old syntax anyway, but the intent was good.
It's worth pointing out that other proprietary styles were given the same treatment. For example, you can use -ms-behavior in IE8 instead of the old behavior style. No-one uses it. Why? I don't really know.
Another fact worth knowing is that the W3C are in the process of standardizing a CSS property called filter. It will do a completely different job to the Microsoft filter style, and work completely differently. If/when it is standardized and browsers start supporting it, there will be an explicit clash between the two syntaxes.
Seems like you answered your own question. Yes they're needed. Microsoft trying to get more in line with the standards means that some versions of IE have their own slightly different syntax rules for the filter property.
In IE7 just filter: followed by the progid:DXIma... etc will work. But for IE8+ there is the IE7 fallback it may use in compatibility mode, and the more proper -ms- prefixed property for filter, denoting a vendor specific css property, and its value inside qoutes.
What harm would it do to leave it in?
If the browser doesn't understand the line of CSS it will just ignore it.
Those two lines of CSS are almost identical. I would hazard a guess that Microsoft decided to change the syntax for proprietary CSS from IE8 onwards utilising the - (hyphen) prefix which other browsers have been using for yonks.
Technically the CSS isn't W3C compliant either way, so another line of proprietary CSS can do no harm.
It's not worth trying to understand IE at the best of times!
Can you use the browser specific prefix in front of all standard tags?
e.g.
#div{
padding:20px;
-moz-padding-bottom:10px;
}
is the above valid CSS for ensuring Firefox has a different bottom padding to all other browsers?
No, it's not a prefix for targetting a browser, it's a prefix that is used for specific non-standard properties like -moz-opacity or -moz-padding-start. It's not available for the standard properties.
First, no, there isn't a prefix for things that are standardized, since they're the same property cross-browser (or should be, don't take this for granted in IE).
Instead of what you're after with this prefix, I'd instead look at a completely different approach...taking out the differences in rendering, instead of trying to fix them, at least as many as possible.
Take a look at a CSS reset stylesheet, to normalize the padding and such across browsers, then look at fixing any remaining quirks.
You can always do it, but the style will be ignored by browsers who don't understand it and the CSS won't pass CSS Validation.
This might be of interest.
-webkit-text-stroke
Works in Firefox browsers as well.
I tried to validate my site's CSS using the W3C CSS Validator. Unfortunately, reset-min.css from YUI framework produced parse error on the string " {*font-size:100%; ".
The validator results.
On further investigation I noticed the following error on Firefox's error console:
Warning: Expected declaration but found '*'. Skipped to next declaration.
I couldn't find any explanation for the meaning of the '*', nor references for a problem in this popular reset CSS.
What am I missing?
This is a hack for IE7 and lower. IE7 and lower will skip the asterisk and continue to parse the CSS as normal. Other browsers will just ignore the entire rule.
As an example, since CSS will use the last declared version of a rule, doing the following will cause IE7 and below to use a font-size of 113%, while other browsers use a font-size of 100% for paragraphs.
p { font-size: 100%; *font-size: 113%; }
There is a little more information at webdevout.net.
Personally, I think that it is acceptable to use such hacks for the purposes of working around the brokenness of IE. Apparently, Yahoo! feels the same way.
It's probably an IE compatibility hack.
There are many CSS syntax errors that some browsers (notably IE 6) will ignore and others won't. Some CSS files will use the errors to make a rule that one browser will see and another browser won't.
EDIT: For a full list, see here. In your particular case, that rule will be seen only by IE 7 or lower.
Is there a list of 'good' clean CSS hacks, which are certain to be future-proof?
For example, zoom:1 is safe, as long as it's only served to IE, and you remember it's there. The very common hack of using child selectors is not safe because IE7 supports them. Using height:1% just feels dirty (but that might just be me).
I know of ie7-js, so IE6 bugs don't worry me much. Also, I'm not looking for a religious debate, just sources.
Thanks for the replies - I've selected the one with best sources as answer.
Thanks also for the suggestions to use separate CSS files, or not to worry about it. I entirely agree with you, and for me, those are givens. But when faced with a layout problem, I want a safe fix that will minimise the risk that I'll have to revisit the problem in $IE or $FF + 1. Sorry I didn't make that clearer.
For the majority of IE bugs I think you're best off using conditional comments around a link to a browser specific stylesheet. It tends to keep things pretty neat and it's quite self documenting.
This is a good place for well-documented and well-tested browser bugs and the hacks allow you to work around them:
http://www.positioniseverything.net/
I've used Peter-Paul Koch's "QuirksMode" website a lot for issues involving CSS and cross-browser compatibility. He tends to frown on browser-specific methods, but he does have a page on CSS Hacks.
Nicole Sullivan (AKA Stubbornella) who works for the Yahoo Performance team suggested in The 7 Habits for Exceptional Perf that you should use the CSS underscore hack to patch up IE6 bugs because:
Hacks should be few and far between.
If you will only have 5-6 hacks (which is already plenty) then it would not make sense placing those in an external file and thereby separating it from its context.
An extra file would lead to performance penalties (Yahoo Best Practices, Rule 1).
It should however be noted that this is not valid CSS.
There's no such thing as a good clean/acceptable [css] hack - always code to Standards, and then use browser+version specific stylesheets for any hacks required to make things work.
For example:
default.css
default.ie6-fix.css
default.ie7-fix.css
default.ff2-fix.css
etc
Then, when new version of a browser are released, copy the previous version's hacks and remove the bits that no longer apply (and add new bits, if necessary).
(Load individual stylesheets using Conditional Comments for IE, and user-agent sniffing for other browsers.)
Underscore-hack for IE6-stuff works quite well, eg.
min-height:50px;
_height:50px;
It doesn't require moving things out of context into new css-files, only IE6 gets them and they're easy to filter out if you should decide to stop supporting IE6. They're also very minimal and won't clutter your CSS that much.
Modifying your CSS for browser-specific support is never wrong - as long as you can easily contain it. As you'll notice, standards-compliant browsers, * cough * everything except MSIE, will never break with future releases. New W3C standards also don't break previous standards, they usually deprecate or extend previous standards at the most.
People have mentioned conditional comments which are great for handling IE. But you'll need a bit more for handling all browsers (mobile, gecko, webkit, opera, etc.). Usually you'll parse the incoming request headers to fetch the browser type and version from the User-Agent param. Based on that you can begin loading your CSS files.
I belive the way most of us do it is by:
First developing for one standards-compliant browser (let's take FF for example)
Once the CSS is complete you approach providig support for IE (this can be easily done with the conditional comments, as perviously mentioned)
First create a CSS file that will fine tune everything for IE6 and any other version below
Then create a CSS file that will handle everything for IE7
Lastly, create a CSS file that will handle everything for IE versions of IE8 and greater
Once IE9 comes out, make sure you set IE8+ handling to IE8 specific, and create a IE9+ CSS file with required fixes
Finally, create an additional CSS file for webkit fixes
If required, you can also create additional files to specifically target Chrome or Safari if required
Concerning browser specific CSS implementations, I usually group all of those in my main css file (you can easily do a search for those and replace them in one document if needed). So if something has to be transparent, I'd set both opacity and filters (MSIE) in the same block. Browsers just ignore implementations they don't support, so your safe. Specific implementations I'd tend to avoid are custom implementations (hey, I like the -moz box above the W3C one, but I just don't want to rely on it).
As it goes with CSS inheritance and overriding, you don't have to redefine all the CSS declarations and definitions in every CSS file. Each consecutively loaded CSS file should only contain the selector and specific definitions required for the fix, and nothing else.
What you end up with in the end is your (huge) main css file and others, containing a few lines each, for specific browser fixes - which sums up to something that's not that very hard to maintain and keep track of. It's a personal preference what browser your base css file will be based off, but usually you'll be targeting a browser that will create the least amount of issues for other browsers (so yes, developing for IE6 would be a very poor decision at that point).
As always, following good practices and being pragmatic and meticulous with selectors and specifics about each class and using frameworks will lead you down the path of goodness with seldom fixes required. Structuring your CSS files is a huge plus unless you want to end up with an unordered meaningless mess.
Centricle has a good list of CSS hacks and their compatibilities.
I don't think you'll find a list of hacks that will be future proof, as know one can tell what stupid thing will be implemented in IE next.
This article is a good summary of CSS hacks: http://www.webdevout.net/css-hacks
Here's a good list of filters that are very stable:
/* Opera */
.dude:read-only { color: green; }
/* IE6/IE7 */
#media,
{
.dude { color: silver;}
}
/* IE8 \0 */
#media all\0
{
.dude { color: brown; }
}
/* IE9 monochrome and \9 */
#media all and (monochrome: 0)
{
.dude { color: pink\9; }
}
/* Webkit */
* > /**/ .dude, x:-webkit-any-link { color:red; }
/*
* > /**/
/* hides from IE7; remove if unneeded */
/* Firefox */
#-moz-document url-prefix()
{
.dude { color: green; }
}
When defining rules, I find it good to allow natural degradation take place, for instance, in CSS3 there is support for RGBA Colour models, but there isn't in CSS2, so I find myself doing:
background-color: #FF0000;
background-color: rgba( 255,0,0, 50% );
So that when the later rule fails on older browsers which don't support it, it will degrade to the previously defined style.
I prefer the global conditional comment technique described by Hiroki Chalfant;
I find it helpful to keep my IE-targeted rules side-by-side with my standards-targeted rules in a single valid stylesheet.