About the text-rendering CSS property

Perhaps one of the most commonly forgotten CSS properties is the text-rendering property, and it's easy to see why; at first glance, this property selector seems rather useless.
But the devil lies in the details,and it turns out this CSS property can actually be quite useful when applied to the appropriate situation.
Take, for example, an older target audience. In such a situation, it is very important to have a legible, fairly large, and properly kerned font. Kerning, for the uninitiated, is the horizontal distance between letters.

A neat test to demonstrate the effect of text-rendering values is to overlay both the 'optimizeLegibility' version and the 'optimizeSpeed' version of the same text.
Here this is done by Trent Walton

The kerning difference of text-rendering values

While the kerning difference may seem subtle and unimportant, it can make a world of difference visually for your site, and help you attract your target audience.

The technical side of things:

Inherited Yes
Default value 'auto'
Effected All Elements
Valid Values auto | optimizeSpeed | optimizeLegibility | geometricPrecision | inherit

Browser Compatibility:

Feature Chrome Firefox(Gecko) Internet Explorer Opera Safari(Webkit)
Basic support for Windows and Linux 4.0 but with multiple bugs 3.0 (1.9) -- -- 5.0 (532.5)
'auto' value Chrome treats this as 'optimizeSpeed' If the font size is below 20px Gecko engines render this as 'optimizeSpeed' and above 20px they use 'optimizeLegibility' -- -- Treats this as 'optimizeSpeed'
'geometricPrecision' value 13 supports true geometric precision, without rounding up or down to the nearest supported font size in the operating system. Introduced in WebKit 535.1 Gecko engines treat this as 'optimizeLegibility' -- -- --