Individual named elements can be identified in the DOM structure readily. But we might have several instances of a particular element. To name all these individually is a fair effort, especially through multiple edits. So the DOM uses collections. A collection is a grouping of all the same tag name elements in a document.
Some collections are images, forms, links and rows.
The images collection holds all the images in a document, the forms collection holds all the forms in a document, the links collection holds all the links in a document, and rows holds all the rows for a table. Some collections have child members, for example forms have elements, and we can address the individual elements of a form through the elements collection of a member of the form collection. There are many more collections, and one important one is the all collection. The all collection holds every element, and is useful for elements that are not directly absorbed into a defined collection. Accessing Collections Collections save us from having to name every HTML element.