This topic lists the clearance constraints:
maxClearance
minCenterLineClearance
minClearance
minClearanceOverLayer
minClusterClearance
minCornerClearance
minCutRoutingClearance
minInnerVertexClearance
minNeighboringShapesClearance
minSameNetClearance
minSideClearance
minTouchingDirectionClearance
minVoltageClearance
shapeRequiredClearance
Tcl Constraint Commands
Manage Constraints