12. A system, comprising: a data processing apparatus; and a computer-readable storage medium coupled to the data processing apparatus and storing a dictionary defining query triggers, each of the query triggers being one or more terms; wherein the computer-readable medium also stores instructions that, when executed by the data processing apparatus, cause the data processing apparatus to perform operations comprising: identifying query triggers in a resource displayed in a web browser application environment on the data processing apparatus, wherein the resource is a non-query resource; for each query trigger identified in the resource, calculating a rank score for the query trigger based on attributes of the query trigger, the attributes including at least one of: a context of the query trigger defined by a display format of the query trigger in the resource; and a frequency of occurrence of the query trigger in the resource; ranking the query triggers according to the rank scores; generating search query suggestions from the query triggers identified in the resource; and presenting the search query suggestions in the web browser application environment according to the ranking of the query triggers.
12. A system, comprising: a data processing apparatus; and a computer-readable storage medium coupled to the data processing apparatus and storing a dictionary defining query triggers, each of the query triggers being one or more terms; wherein the computer-readable medium also stores instructions that, when executed by the data processing apparatus, cause the data processing apparatus to perform operations comprising: identifying query triggers in a resource displayed in a web browser application environment on the data processing apparatus, wherein the resource is a non-query resource; for each query trigger identified in the resource, calculating a rank score for the query trigger based on attributes of the query trigger, the attributes including at least one of: a context of the query trigger defined by a display format of the query trigger in the resource; and a frequency of occurrence of the query trigger in the resource; ranking the query triggers according to the rank scores; generating search query suggestions from the query triggers identified in the resource; and presenting the search query suggestions in the web browser application environment according to the ranking of the query triggers. 13. The system of claim 12 , wherein: the query triggers include expansion terms, the expansion terms for each query trigger being terms that are query expansions of the one or more terms of the query trigger; and identifying the query triggers in the resource comprises searching the resource for the query triggers included in the dictionary; and generating search query suggestions from the query triggers comprises generating for a query trigger identified in the resource a search query that includes an expansion term of the query trigger.