2.1.8 [CSS-Level2-2009] Section 4.3.2, Lengths
The format of a length value (denoted by <length> in this specification) is a <number> (with or without a decimal point) immediately followed by a unit identifier (e.g., px, em, etc.). After a zero length, the unit identifier is optional.
Quirks Mode and IE7 Mode (All Versions)
Lengths can be specified in scientific notation; for example, ‘5e2px’ instead of ‘500px’.
Quirks Mode (All Versions)
Spaces are allowed between
and the unit identifier.