diff --git a/doc/internals/body-parsing.txt b/doc/internals/body-parsing.txt
index e9c8b4b..5baa549 100644
--- a/doc/internals/body-parsing.txt
+++ b/doc/internals/body-parsing.txt
@@ -67,12 +67,17 @@
            automatically adjusted to the number of bytes already inspected.
 
 msg.sov  : start of value. First character of the header's value in the header
-           states, start of the body in the data states until headers are
-           forwarded. This offset is automatically adjusted when inserting or
-           removing some headers. In data states, it always constains the size
-           of the whole HTTP headers (including the trailing CRLF) that needs
-           to be forwarded before the first byte of body. Once the headers are
-           forwarded, this value drops to zero.
+           states, start of the body in the data states. Strictly positive
+           values indicate that headers were not forwarded yet (<buf.p> is
+           before the start of the body), and null or positive values are seen
+           after headers are forwarded (<buf.p> is at or past the start of the
+           body). The value stops changing when data start to leave the buffer
+           (in order to avoid integer overflows). So the maximum possible range
+           is -<buf.size> to +<buf.size>. This offset is automatically adjusted
+           when inserting or removing some headers. It is useful to rewind the
+           request buffer to the beginning of the body at any phase. The
+           response buffer does not really use it since it is immediately
+           forwarded to the client.
 
 msg.sol  : start of line. Points to the beginning of the current header line
            while parsing headers. It is cleared to zero in the BODY state,
@@ -97,7 +102,8 @@
            states nor by forwarding.
 
 The beginning of the message headers can always be found this way even after
-headers have been forwarded :
+headers or data have been forwarded, provided that everything is still present
+in the buffer :
 
             headers = buf.p + msg->sov - msg->eoh - msg->eol