how does X11 get EDID?

[Sanford Rockowitz]

Can someone point me to where in the X11 code base the the monitor is
queried for the EDID?

As background, I am the developer of ddcutil (www.ddcutil.com), a
program to control monitor settings using DDC.   I have a user bug
report showing that the EDID obtained from slave address x50 on the I2C
bus differs from that obtained from X11 using calls to
XRRGetOutputProperty() for atoms EDID, EDID_DATA, and
XFree86_DDC_EDID_RAWDATA. (The first atom found is used.)  In
particular, the latter contains a Display Descriptor of type FF (Display
Product Serial Number), the former does not.  I am trying to understand
why this is happening.

I have found one old mailing list posting
(https://lists.freedesktop.org/archives/xorg/2008-September/038605.html)
that refers to a "cooked" EDID, which suggests that X11 is performs some
EDID manipulation. 

Thanks in advance,
Sanford