This part is associated with Zinc Finger Nuclease devices
A zinc finger nuclease is an engineered protein derived from two zinc finger DNA binding proteins and cutting domains usually from a type IIS restriciton enzyme. The special thing about them is that 1) they bind long sequences of DNA, long enough that it might be unique in a eukaryotic genome, and 2) zinc finger proteins that bind to most sequences can be generated somewhat easily. So, you can use a zinc finger nuclease to introduce a ds break at a specific user-defined site in a eukaryotic genome if the protein is delivered to the nucleus of the cell. Eukaryotic ds breaks stimulate homologous recombination. So, if you deliver both the ZFN and a DNA homologous to the target site, you get insertion of your DNA into that site of the genome.
You should read the following papers
References: PMID 18545224, PMID 17603475, PMID 11821858