white-space: pre-line @ CSS = invalid

Hello,

sorry for my bad english.
I tried to validate following lines

article pre {
    margin-left: -5em;
    white-space: pre-line;
}

Settings were standard, except Profile. There I have chosen CSS level 3

This should validate (http://www.w3.org/TR/css3-text – 4.4 White Space and 
Text Wrapping Shorthand: the ‘white-space’ property)

but it shows the failure:
Ungültige Nummer : white-space pre-line ist kein white-space-Wert : pre-line 
pre-line

I hope you know what I wanted to say

Greetings
Emma