Layout size sharing in a grid layout for a user interface

Described is an information sharing method and mechanism used by a layout system to share information across related column and row user interface elements (corresponding to definitions). Definitions of a table or grid are grouped together with respect to sizing via a common group name. Scope values may be used to limit the grouping to selected subtrees of elements. When layout occurs, size sharing information is determined for the group-related definitions via a common size sharing object. Grouped definitions thus may be sized to the largest content to display of any one element. Elements corresponding to definitions may be manually sized by a user, or may be based on the size of a defined master element, such as the width of a header. The scope value of a group may be changed dynamically, such as by user interaction, which may cause groups to merge or split.