[Gate-users] setx3length and setX4Length about MLC

[????]

Dear Gates,
 Is there any detailed description about  MLC design. I come into some problem of  multileaf collimator macro sentence ,such as setx3length or setX4Length, there is no explain on the website, any one can give me a clue?  The is following:
/gate/mylinac_MLC_Leaf1_Left/daughters/name mylinac_MLC_Leaf1_Left_trp_sup

/gate/mylinac_MLC_Leaf1_Left/daughters/insert general_trpd

/gate/mylinac_MLC_Leaf1_Left_trp_sup/setMaterial AcceleratorCollimatorLeafMaterial

/gate/mylinac_MLC_Leaf1_Left_trp_sup/geometry/setX1Length 16 mm

/gate/mylinac_MLC_Leaf1_Left_trp_sup/geometry/setX2Length 16 mm

/gate/mylinac_MLC_Leaf1_Left_trp_sup/geometry/setX3Length 162.60 mm

/gate/mylinac_MLC_Leaf1_Left_trp_sup/geometry/setX4Length 162.60 mm

/gate/mylinac_MLC_Leaf1_Left_trp_sup/geometry/setY1Length 3 mm

/gate/mylinac_MLC_Leaf1_Left_trp_sup/geometry/setY2Length 3 mm

/gate/mylinac_MLC_Leaf1_Left_trp_sup/geometry/setZLength  31.77 mm

/gate/mylinac_MLC_Leaf1_Left_trp_sup/geometry/setTheta    66.567 deg ??Z???

/gate/mylinac_MLC_Leaf1_Left_trp_sup/geometry/setPhi  0 deg  ?xy??

/gate/mylinac_MLC_Leaf1_Left_trp_sup/geometry/setAlp1     0 deg

/gate/mylinac_MLC_Leaf1_Left_trp_sup/geometry/setAlp2     0 deg

/gate/mylinac_MLC_Leaf1_Left_trp_sup/placement/setTranslation    -38.38 0.0 21.615 mm

#/gate/mylinac_MLC_Leaf1_Left_trp_sup/placement/setTranslation     28.63 0.0 15.885 mm