15. A non-transitory computer storage medium encoded with a computer program, the program comprising instructions that when executed by a data processing apparatus cause the data processing apparatus to perform operations comprising: identifying a seed query for a structured document based on a performance of the seed query with respect to the structured document; identifying one or more embedded coding fragments for the structured document using the seed query, each identified embedded coding fragment specifying a structure of a portion of the structured document that includes at least one term of the seed query; generating one or more query templates, each query template corresponding to at least one of the identified embedded coding fragments, the query template including the structure of the corresponding at least one embedded coding fragment and a generative rule to be used in generating one or more synthetic queries; generating the one or more synthetic queries using the one or more query templates and other structured documents, the generating comprising, for each query template: identifying a portion of a particular structured document that includes the structure specified by the corresponding embedded coding fragment; and generating a synthetic query using text contained in the portion of the particular structured document and specified by the generative rule; and storing, at least one of the one or more synthetic queries in a query store.
15. A non-transitory computer storage medium encoded with a computer program, the program comprising instructions that when executed by a data processing apparatus cause the data processing apparatus to perform operations comprising: identifying a seed query for a structured document based on a performance of the seed query with respect to the structured document; identifying one or more embedded coding fragments for the structured document using the seed query, each identified embedded coding fragment specifying a structure of a portion of the structured document that includes at least one term of the seed query; generating one or more query templates, each query template corresponding to at least one of the identified embedded coding fragments, the query template including the structure of the corresponding at least one embedded coding fragment and a generative rule to be used in generating one or more synthetic queries; generating the one or more synthetic queries using the one or more query templates and other structured documents, the generating comprising, for each query template: identifying a portion of a particular structured document that includes the structure specified by the corresponding embedded coding fragment; and generating a synthetic query using text contained in the portion of the particular structured document and specified by the generative rule; and storing, at least one of the one or more synthetic queries in a query store. 16. The non-transitory computer storage medium of claim 15 , wherein: the query has been identified as a seed query based on a performance of the query; and the instructions cause the data processing apparatus to perform further operations comprising identifying the structured document by determining that search results that reference the structured document have been selected at least a threshold number of times.