no parameter in first segment of relative URI?

Dear URI experts,

Looking through the URI syntax in detail, I became aware
of the following 'anomaly': parameters are not allowed
in the first segment of a relative URI (if it doesn't start
with a slash). The relevant rules are:

  relativeURI   = ( net_path | abs_path | rel_path ) [ "?" query ]

  net_path      = "//" authority [ abs_path ]
  abs_path      = "/"  path_segments
  rel_path      = rel_segment [ abs_path ]

  rel_segment   = 1*( unreserved | escaped |
                      ";" | "@" | "&" | "=" | "+" | "$" | "," )

  path_segments = segment *( "/" segment )
  segment       = *pchar *( ";" param )
  param         = *pchar
  pchar         = unreserved | escaped |
                  ":" | "@" | "&" | "=" | "+" | "$" | ","

So in "abc;def/ghi;jkl", 'jkl' is a parameter, but 'def' isn't.
On the other hand, in "/abc;def/ghi;jkl", both 'def' and 'jkl'
are parameters.

Is this an error in the syntax, or can somebody explain this?


Regards,     Martin.