12. A system comprising: a user interface device; and one or more server computers operable to interact with the user interface device and to: apply a pre-defined rule set to each indexable document in a plurality of structured documents, including to apply the pre-defined rule set to a plurality of versions of an indexable document in the plurality of structured documents, to extract one or more index values, the pre-defined rule set including a plurality of rules, each rule having a distinct rule identifier, each extracted index value being extracted by a rule in the pre-defined rule set, wherein one or more versions of the indexable document is concurrently accessible to a plurality of users for collaborative authoring; and for each extracted index value, store in an index-value data structure the extracted index-value, the rule identifier of the rule that extracted the index value, and information identifying the respective indexable document and a respective version of the respective indexable document from which the index-value was extracted.
12. A system comprising: a user interface device; and one or more server computers operable to interact with the user interface device and to: apply a pre-defined rule set to each indexable document in a plurality of structured documents, including to apply the pre-defined rule set to a plurality of versions of an indexable document in the plurality of structured documents, to extract one or more index values, the pre-defined rule set including a plurality of rules, each rule having a distinct rule identifier, each extracted index value being extracted by a rule in the pre-defined rule set, wherein one or more versions of the indexable document is concurrently accessible to a plurality of users for collaborative authoring; and for each extracted index value, store in an index-value data structure the extracted index-value, the rule identifier of the rule that extracted the index value, and information identifying the respective indexable document and a respective version of the respective indexable document from which the index-value was extracted. 13. The system of claim 12 , wherein the one or more server computers are further operable to: identify each document in the plurality of structured documents that has an indexing property that matches a stored reference indexing property as an indexable document; and determine for each indexable document whether the respective indexable document is locked.