some question about portal in xml

    I am new in CS.
    I used blender to build two sectors and portals and I used the portals to connect the two sectors. After I exported the model to XML file, I found some tags in the XML that I have never seen before, the code is followed:

<library>
<meshfact name='genCube.004'>
<plugin>genmeshfact</plugin>
<zuse/>
    <params>
     <material>misc_o023.jpg</material>
     <v x="1.95" y="-4.95" z="2.525" u="0.000000" v="-1.000000" nx="-2.38419e-007" ny="1" nz="4.59341e-014"/>
     <v x="1.95" y="-4.95" z="5" u="0.000000" v="0.000000" nx="-2.38419e-007" ny="1" nz="4.59341e-014"/>
     <v x="-0.0499992" y="-4.95" z="5" u="1.000000" v="0.000000" nx="-2.38419e-007" ny="1" nz="4.59341e-014"/>
     <v x="-0.0499997" y="-4.95" z="2.525" u="1.000000" v="-1.000000" nx="-2.38419e-007" ny="1" nz="4.59341e-014"/>
     <t v1="3" v2="2" v3="1"/>   
     <t v1="3" v2="1" v3="0"/>
……
    </params>
  </meshfact>
</library>

  What is the meaning of "u", "v", "nx", "ny", "nz" in the XML?
       Is any document that explain the particular meaning of tags in XML (except "Breakdown of an XML World File" which is provided in the site)?

[jorrit]

This has nothing to do with portals. The object that you are looking at in the xml is a genmesh with name genCube.004. The parameters u,v are for texture mapping. nx, ny, nz are normals.

Greetings,

This has nothing to do with portals. The object that you are looking at in the xml is a genmesh with name genCube.004. The parameters u,v are for texture mapping. nx, ny, nz are normals.

Greetings,

    nx, ny, nz are normals. But what are the meaning of nx, ny, nz?  they are used for what purpose?

[jorrit]

They represent the normal pointing away from the surface at that specific point. They are used for lighting.

Greetings,