(PECL solr >= 0.9.2)
SolrInputDocument::merge — Merges one input document into another
Merges one input document into another.
sourceDocThe source document.
overwrite
       If this is TRUE it will replace matching fields in the destination document.
      
   Возвращает TRUE в случае успешного завершения  или FALSE в случае возникновения ошибки. In the future, this will be modified to return the number of fields in the new document.