Methods, systems, and apparatus, including computer programs encoded on one or more computer storage media, for modifying content layout for an electronic document are described. In one aspect, a method includes receiving an identification of a subset of content items identified in a first electronic document. Each content item in the subset of content items includes displayable data. A prioritization of the subset of content items is identified, and a first content item is selected based on the prioritization. A new value of a first layout property for the selected content item is calculated based at least in part on one or more initial values. A new electronic document is generated. The new electronic document includes an identification of the new value and data for generating a second graphical representation of the subset of content items based at least in part on the new value.