breakpointDef — Defines breakpoint sets to be used in model
breakpointDef :  [name],  bpID,  [units]
     (description?, bpVals)
| name (optional) - the name of the breakpoint set | 
| bpID - the internal, document-unique XMLname for the breakpoint set | 
| units (optional) - the units of measure for the breakpoint set | 
A breakpointDef is where gridded table breakpoints are given. Since these are separate from function data, may be reused.
| DAVEfunc | 
| description | 
| bpVals |