code: func (col *column) parseColumnComment() {
  	comment := strings.TrimSpace(col.comment)
  	start := strings.Index(comment, "[[")
  	end := strings.Index(comment, "]]")
  	var content string
  	if start < end {
  		content = comment[start+2 : end]
  	}
  
  	fields := strings.Split(content, ";")
  	for _, field := range fields {
  		field = strings.TrimSpace(field)
  		kvs := strings.Split(field, "=")
  		col.parseRule(kvs)
  	}
  }
docs: // parse the data rules.
  // rules like `a int unique comment '[[range=1,10;step=1]]'`,
  // then we will get value from 1,2...10