code: func (p Pages) RelatedIndices(doc related.Document, indices ...interface{}) (Pages, error) {
  	indicesStr, err := cast.ToStringSliceE(indices)
  	if err != nil {
  		return nil, err
  	}
  
  	result, err := p.searchDoc(doc, indicesStr...)
  	if err != nil {
  		return nil, err
  	}
  
  	if page, ok := doc.(Page); ok {
  		return result.removeFirstIfFound(page), nil
  	}
  
  	return result, nil
  
  }
docs: // RelatedIndices searches the given indices with the search keywords from the
  // supplied document.