[FieldTrip] PLV definition and implementation

[Natalia Grion]

Dear Fieldtripers, I would like to know how you define and implement  
'plv' (phase locking value) in the fieldtrip. I do not see any  
documentation on this issue of reference paper and I'm confused by the  
fact that this definition was used by Lachaux (1999) and fieldtrip is  
taking the cross-spectrum and doing some treatment (difficult to  
follow in the series of functions involved) to ignore amplitude  
consistency (I guess a different treatment from coherence 'coh'  
function).
Could you clarify this to me or give me a reference paper?
Thanks!
Natalia