[Gmsh] ask for a help

[亓欣波]

Dear Christophe and Jean:
 I am writing to you for a kind help.
Ｗhen I read the introduction to MSH ASCII file format, I feel some confused about below:
     $Elements      2                      two elements:      1 3 2 99 2 1 2 3 4       quad #1: type 3, physical 99, elementary 2, nodes 1 2 3 4      2 3 2 99 2 2 5 6 3       quad #2: type 3, physical 99, elementary 2, nodes 2 5 6 3      $EndElements

what does the "2" mean?
I can't find the references about this number.

Thanks very much!
I am looking forwards to your letter.

Best wishes!

Yours sincerely
Qi Xinbo
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