18. The system as recited in claim 11 , wherein the style information that is external to the source document comprises Cascading Style Sheet (CSS) information.
11. A system comprising: one or more processors; and computer-readable media comprising instructions that are executable by the one or more processors to implement a user interface that is operable to: present, in a first portion of the user interface, source content comprising part of a source document; present, in a second portion of the user interface and concurrently with the source content presented in the first portion of the user interface, markup and style information from a source of style information that is used to style an identified portion of the source content for display, the markup and style information presented responsive to identification by a user of the portion of source content from the first portion of the user interface, and the corresponding markup and style information that will be extracted from the source of style information being highlighted in the second portion of the user interface responsive to receiving a user input to copy the identified portion of source content; and receive a different user input to paste the identified portion of source content into target content with the corresponding markup and style information applied, the corresponding style information demarcated separately from elements of the corresponding markup that define the identified portion of source content that is copied and pasted, and the corresponding style information including style information that is external to the source document.