I noticed this woo theme for example has it set on the HTML tag and therefore the whole site's text has it set. I read that it can cause performance problems but that was a while ago. Some people suggested only adding it to headers and big text.
Have the rules changed now? Do browsers perform well with it?
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I've just fixed a bug where Chrome was refusing to render web fonts (it always fell back to a non-web one, for no reason we could discern). In the end - after considerable amount of head-scratching - the problem was fixed by setting text-rendering from optimizeLegibility (which had been set by Twitter Bootstrap, for what it's worth) to auto.
So I would say for the moment the answer is probably "no". Which isn't to say don't use it, but don't apply it to everything. Use it where needed and test it carefully for weirdnesses or unexpected effects (especially in Chrome!).
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No: there have been many bugs over the years on various platforms which cause text not to be displayed or displayed incorrectly (see below). If your goal is to enable ligatures, there's actually standard property font-variant-ligatures defined in CSS Fonts Level 3 which offers full control:
font-variant-ligatures: common-ligatures;
font-variant-ligatures: common-ligatures discretionary-ligatures historical-ligatures;
See font-variant for other typographic features which can be enabled such as small caps, alternate letter forms, etc.
Before font-variant-ligatures & the related properties were added, the older font-feature-settings property allowed the same feature to be enabled. This is a lower-level interface and is no longer recommended except to enable OpenType features which do not have a higher-level interface.
http://blog.fontdeck.com/post/15777165734/opentype-1 has a simple example:
h1 {
-webkit-font-feature-settings: "liga", "dlig";
-moz-font-feature-settings: "liga=1, dlig=1";
-ms-font-feature-settings: "liga", "dlig";
font-feature-settings: "liga", "dlig";
}
http://elliotjaystocks.com/blog/the-fine-flourish-of-the-ligature/ has more discussion as well.
The popular HTML5 Boilerplate project removed it two years ago due to various rendering problems:
https://github.com/h5bp/html5-boilerplate/issues/78
Two Chromium bugs which I just fixed this morning caused Chrome 21 on Windows XP to either fail to perform font substitution at all, displaying the missing character symbol rather than using one from a different font, and displaying text incorrectly overlapping other elements:
http://code.google.com/p/chromium/issues/detail?id=114719
http://code.google.com/p/chromium/issues/detail?id=149548
See http://aestheticallyloyal.com/public/optimize-legibility/ for a few other concerns.
http://bocoup.com/weblog/text-rendering/ highlighted compatibility problems on Android and general performance issues
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text-rendering: optimizeLegibility; was used in one of our web apps. it rendered properly in all browsers, except one - chrome (64) on windows 7.
Had to remove the property as most of our end users were from that category.
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CSS text-rendering looks shaky. Instead of grinding time with a poor CSS property, it may be worthwhile to go with this...
If Javascript is an option for you, Kerning.js looks promising, a javascript approach to kerning and kerning pairs hosted on Github.
Also worth noting, if you are getting serious about typography, there is Font Squirrel free use web fonts.
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using "text-rendering: optimizelegibility" also causes rendering errors in android native browser (4.2 & 4.3). If you use this attribute in combination with loading new fonts via @font-face, the font will not display at all (only fallback). without "text-rendering: optimizelegibility" and @font-face the font loads and gets displayed as expected.
from the MDN text-rendering page, last updated on 18:27, 29 Apr 2012, it reads:
which tels us that it is not defined in any CSS standard, thus leading to cross-browser issues, as seen on the Browser compatibility table.
By default
So, is safe to assume that the best option is to let the browser take care of details like this, since this feature is not a standard (yet), and most browsers don't support it.