E-values calculation (MEME)

Question

[anahochmanova]

I'm trying to understand how MEME's E-values are calculated but can't find how could I reproduce a simple case with a few sequences, a PSPM and an E-value calculation.

Tried to find some source code of an implementation to try to debug it but was not able, please is somewhere an example of how to calculate MEME's E-values? Or an explanation of how they can be calculated?

http://www.sdsc.edu/~tbailey/MEME-protocol-draft2/protocols.html

MEME reports an E-value for each motif it finds, which is an estimate of the number of (equally or more interesting) motifs one would expect to find by chance if the letters in the input sequences were shuffled. Motifs with small E-values (e.g., less than 0.001) are very unlikely to be random sequence artifacts.