code: func (bb *Builder) CapCreationTime() *Builder {
  	ctime, ok := bb.m["unixCtime"].(string)
  	if !ok {
  		return bb
  	}
  	mtime, ok := bb.m["unixMtime"].(string)
  	if ok && ctime > mtime {
  		bb.m["unixCtime"] = mtime
  	}
  	return bb
  }
docs: // CapCreationTime caps the "unixCtime" field to be less or equal than "unixMtime"