code: func (c *DefaultIndexingChain) perField(name string) *PerField {
  	hashPos := util.Hashstr(name) & c.hashMask
  	fp := c.fieldHash[hashPos]
  	for fp != nil && fp.fieldInfo.Name != name {
  		fp = fp.next
  	}
  	return fp
  }
docs: /*
  Returns a previously created PerField, or nil if this field name
  wasn't seen yet.
  */