16. On a computing device, a method for presenting a user interface, the method comprising: receiving a request to display a list of items, each item of the list of items comprising a plurality of parts each having an appearance defined by a corresponding portion of a full version template comprising a markup document; for an item in the list of items, populating each portion of the full version template to render a full version of a representation of the item; identifying one or more tags in the full version template, the one or more tags specifying one or more corresponding portions of the full version template included within a subset of the plurality of parts; extracting the one or more portions of the full version template specified by the one or more tags to generate a preview placeholder template, the preview placeholder template defining an appearance of a thin version of a list item representation, the preview placeholder template comprising a subset of items of the full version template tagged for inclusion in the preview placeholder template, the subset of items comprising fewer items than the full version template; storing the preview placeholder template; and in a later request for scrolling the list of items, retrieving the preview placeholder template from storage and populating the preview placeholder template with data to render and display a thin version of the representation of one or more items of the list of items initially during scrolling, the thin version for each item of the one or more items comprising a default item for a field of metadata in place of an omitted item from the full version, and then at a later time replacing the thin version of the one or more items in the list of items with the full version of the one or more items in the list of items.
16. On a computing device, a method for presenting a user interface, the method comprising: receiving a request to display a list of items, each item of the list of items comprising a plurality of parts each having an appearance defined by a corresponding portion of a full version template comprising a markup document; for an item in the list of items, populating each portion of the full version template to render a full version of a representation of the item; identifying one or more tags in the full version template, the one or more tags specifying one or more corresponding portions of the full version template included within a subset of the plurality of parts; extracting the one or more portions of the full version template specified by the one or more tags to generate a preview placeholder template, the preview placeholder template defining an appearance of a thin version of a list item representation, the preview placeholder template comprising a subset of items of the full version template tagged for inclusion in the preview placeholder template, the subset of items comprising fewer items than the full version template; storing the preview placeholder template; and in a later request for scrolling the list of items, retrieving the preview placeholder template from storage and populating the preview placeholder template with data to render and display a thin version of the representation of one or more items of the list of items initially during scrolling, the thin version for each item of the one or more items comprising a default item for a field of metadata in place of an omitted item from the full version, and then at a later time replacing the thin version of the one or more items in the list of items with the full version of the one or more items in the list of items. 18. The method of claim 16 , wherein storing the preview placeholder template comprises temporarily storing the preview placeholder in a memory cache of the computing device.