17. A non-transitory computer-readable medium storing software comprising instructions executable by one or more computers which, upon such execution, cause the one or more computers to perform operations comprising: identifying a plurality of different document versions of a particular document; identifying a first type of metadata that is associated with each document version of the plurality of different document versions, wherein the first type of metadata includes data that describes a source that provides each document version of the plurality of different document versions; identifying, by the computer system, at least a second type of metadata that is associated with each document version of the plurality of different document versions, wherein the second type of metadata describes a feature of each document version of the plurality of different document versions other than the source of the document version; for each document version of the plurality of different document versions, applying a priority rule to the first type of metadata and the second type of metadata, to generate a priority value generated for each document version of the plurality of different document versions; selecting a particular document version, of the plurality of different document versions, based on the priority values; and providing the particular document version for presentation.
17. A non-transitory computer-readable medium storing software comprising instructions executable by one or more computers which, upon such execution, cause the one or more computers to perform operations comprising: identifying a plurality of different document versions of a particular document; identifying a first type of metadata that is associated with each document version of the plurality of different document versions, wherein the first type of metadata includes data that describes a source that provides each document version of the plurality of different document versions; identifying, by the computer system, at least a second type of metadata that is associated with each document version of the plurality of different document versions, wherein the second type of metadata describes a feature of each document version of the plurality of different document versions other than the source of the document version; for each document version of the plurality of different document versions, applying a priority rule to the first type of metadata and the second type of metadata, to generate a priority value generated for each document version of the plurality of different document versions; selecting a particular document version, of the plurality of different document versions, based on the priority values; and providing the particular document version for presentation. 23. The computer-readable medium of claim 17 , wherein the first type of metadata includes an address of a server that provides each document version of the plurality of different versions.