What is claimed is:1. A method performed by a data processing apparatus, the method comprising:receiving content displayed within a display environment that is displayed on a user device as the content is being typed into the display environment by a user;determining, while receiving a first portion of the content being typed in the display environment that is displayed on a user device, and based on a second portion of the content that (i) was previously typed and (ii) is behind an input cursor included in the display environment, a first factual entity related to the second portion of content that is behind the input cursor;after determining the first factual entity and while receiving a third portion of the content being typed and based on (i) the first portion of the content that was previously typed and (ii) the second portion content that was previously typed, that both collectively comprise an updated portion of content that occurs in the display environment, determining a second factual entity that is related to the first portion of the content, the second portion of the content, and the third portion of the content, the determining the second factual entity comprising:determining that a measured level of intent for the third portion of the content is greater than a threshold level of intent; andin response to determining that the measured level of intent for the third portion of the content is greater than the threshold level of intent, determining the second factual entity that is related to the first portion of the content, the second portion of the content, and the third portion of the content;requesting, for a user interface element, content that is related to both the first factual entity and the second factual entity, wherein the user interface element provides a collection of content related to the first factual entity and the second factual entity within the display environment;receiving the content of the user interface element for contemporaneous display on the user device with the content of the display environment; andproviding, to the user device, instructions to cause display of the content in the user interface element with the display environment.2. The method of claim 1, the method further comprising:providing, to the user device, instructions to cause display of the first factual entity and the second factual entity with the content of the user interface element.3. The method of claim 1, wherein the display environment is a document display environment, and wherein the document display environment displays a document authored by the user.4. The method of claim 1, further comprising:after providing instructions to cause display of the content of the user interface element with the display environment:receiving additional content that is typed in the display environment after the first portion of the content that was typed in the display environment;determining, in response to the additional content, a third factual entity related to the additional content;requesting, for the user interface element, updated content that is related to the first factual entity, the second factual entity, and the third factual entity;receiving the updated content of the user interface element for contemporaneous display on the user device with the content of the display environment; andproviding, to the user device, instructions to cause display of the updated content in the user interface element with the display environment.5. The method of claim 1, wherein:the user interface element comprises an input element configured to receive input from the user device; andthe method further comprises:receiving an indication that the user device supplied input to input element; andinserting a portion of the content displayed in the user interface element into the content of the display environment.6. A non-transitory computer storage medium encoded with computer program instructions that, when executed by one or more processors, cause a computer device to perform operations comprising:receiving content displayed within a display environment that is displayed on a user device as the content is being typed into the display environment by a user;determining, while receiving a first portion of the content being typed in the display environment that is displayed on a user device, and based on a second portion of the content that (i) was previously typed and (ii) is behind an input cursor included in the display environment, a first factual entity related to the second portion of content that is behind the input cursor;after determining the first factual entity and while receiving a third portion of the content being typed and based on (i) the first portion of the content that was previously typed and (ii) the second portion content that was previously typed, that both collectively comprise an updated portion of content that occurs in the display environment, determining a second factual entity that is related to the first portion of the content, the second portion of the content, and the third portion of the content, the determining the second factual entity comprising:determining that a measured level of intent for the third portion of the content is greater than a threshold level of intent; andin response to determining that the measured level of intent for the third portion of the content is greater than the threshold level of intent, determining the second factual entity that is related to the first portion of the content, the second portion of the content, and the third portion of the content;requesting, for a user interface element, content that is related to both the first factual entity and the second factual entity, wherein the user interface element provides a collection of content related to the first factual entity and the second factual entity within the display environment;receiving the content of the user interface element for contemporaneous display on the user device with the content of the display environment; andproviding, to the user device, instructions to cause display of the content in the user interface element with the display environment.7. The non-transitory computer storage medium of claim 6, the method further comprising:providing, to the user device, instructions to cause display of the first factual entity and the second factual entity with the content of the user interface element.8. The non-transitory computer storage medium of claim 6, wherein the display environment is a document display environment, and wherein the document display environment displays a document authored by the user.9. The non-transitory computer storage medium of claim 6, the operations further comprising:after providing instructions to cause display of the content of the user interface element with the display environment:receiving additional content that is typed in the display environment after the first portion of the content that was typed in the display environment;determining, in response to the additional content, a third factual entity related to the additional content;requesting, for the user interface element, updated content that is related to the first factual entity, the second factual entity, and the third factual entity;receiving the updated content of the user interface element for contemporaneous display on the user device with the content of the display environment; andproviding, to the user device, instructions to cause display of the updated content in the user interface element with the display environment.10. The non-transitory computer storage medium of claim 6, wherein:the user interface element comprises an input element configured to receive input from the user device; andthe operations further comprises:receiving an indication that the user device supplied input to input element; andinserting a portion of the content displayed in the user interface element into the content of the display environment.11. A system comprising:one or more processors configured to execute computer program instructions; andcomputer storage media encoded with computer program instructions that, when executed by one or more processors, cause a computer device to perform operations comprising:receiving content displayed within a display environment that is displayed on a user device as the content is being typed into the display environment by a user;determining, while receiving a first portion of the content being typed in the display environment that is displayed on a user device, and based on a second portion of the content that (i) was previously typed and (ii) is behind an input cursor included in the display environment, a first factual entity related to the second portion of content that is behind the input cursor;after determining the first factual entity and while receiving a third portion of the content being typed and based on (i) the first portion of the content that was previously typed and (ii) the second portion content that was previously typed, that both collectively comprise an updated portion of content that occurs in the display environment, determining a second factual entity that is related to the first portion of the content, the second portion of the content, and the third portion of the content, the determining the second factual entity comprising:determining that a measured level of intent for the third portion of the content is greater than a threshold level of intent; andin response to determining that the measured level of intent for the third portion of the content is greater than the threshold level of intent, determining the second factual entity that is related to the first portion of the content, the second portion of the content, and the third portion of the content;requesting, for a user interface element, content that is related to both the first factual entity and the second factual entity, wherein the user interface element provides a collection of content related to the first factual entity and the second factual entity within the display environment;receiving the content of the user interface element for contemporaneous display on the user device with the content of the display environment; andproviding, to the user device, instructions to cause display of the content in the user interface element with the display environment.12. The system of claim 11, the method further comprising:providing, to the user device, instructions to cause display of the first factual entity and the second factual entity with the content of the user interface element.13. The system of claim 11, wherein the display environment is a document display environment, and wherein the document display environment displays a document authored by the user.14. The system of claim 11, the operations further comprising:after providing instructions to cause display of the content of the user interface element with the display environment:receiving additional content that is typed in the display environment after the first portion of the content that was typed in the display environment;determining, in response to the additional content, a third factual entity related to the additional content;requesting, for the user interface element, updated content that is related to the first factual entity, the second factual entity, and the third factual entity;receiving the updated content of the user interface element for contemporaneous display on the user device with the content of the display environment; andproviding, to the user device, instructions to cause display of the updated content in the user interface element with the display environment.15. The system of claim 11, wherein:the user interface element comprises an input element configured to receive input from the user device; andthe operations further comprises:receiving an indication that the user device supplied input to input element; andinserting a portion of the content displayed in the user interface element into the content of the display environment.