[BioC] question regarding genefilter package

[zrl]

Dear list,
I am bit confused about the meaning of "var.cutoff" in function of
"nsFilter". Since we calculate the IQR of each gene, how could the
var.cutoff is a absolute value, 0.5.
When I read the help document, it says "Note that by default the
numerical-filter cutoff is interpreted as a quantile..." Does it mean
we really compare the IQR with region of quantile 0 to quantile 0.5?
Could someone help me clarify this? Thanks.