The kerning option of microtype

I wonder what the kerning option of the microtype package does? In the manual it says that kerning=true will give additional kerning. But how? Is this something that has to be specified in addition to activating the option?

I can see no visual difference or any difference in filesize when compiling the two following examples with pdfTeX-1.40.10. Example 1:

\documentclass{article}

\usepackage{lipsum}
\usepackage[kerning=true]{microtype}

\begin{document}

\lipsum[1-5]

\end{document}


Example 2:

\documentclass{article}

\usepackage{lipsum}
\usepackage[kerning=false]{microtype}

\begin{document}

\lipsum[1-5]

\end{document}

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My opinion is, switch off everything except Character protrusion. Most of the typographers agree, that Font expansion distorts the font. Personally, I see it, and I agree - the distortion is quite visible for the trained reader. Tracking/letterspacing changes the color of the words. It's especially confusing in the Cyrillic typography, where spacing out is used for emphasis instead of italics - soul package. –  Karl Karlsson Jun 15 '11 at 9:20
@KarlKarlsson I've asked a question about the greatest value for font expansion for which distortion is not noticeable: tex.stackexchange.com/questions/30949/… –  N.N. Oct 8 '11 at 17:53

kerning is not a "true-false" option. Its purpose is to add some kerning independently of the adjacent letters, for example to set the French semicolon that needs a space before it. However it's not working well: for example, the colon requires a normal interword space before and after it, and this space should stretch or shrink along with the other spaces on the same line, which is impossible to get with kerning.