Non-standard
This feature is non-standard and is not on a standards track. Do not use it on production sites facing the Web: it will not work for every user. There may also be large incompatibilities between implementations and the behavior may change in the future.
Summary
The ::-ms-value pseudo-element applies rules to the value/content of an <input> or a <select>. Only certain properties can be set on this pseudo-element; others will have no effect.
Syntax
input::-ms-value { style properties }
select::-ms-value { style properties }
Specifications
Not part of any specification.
Microsoft has a description on MSDN.