On disk, an Eclipse based product is structured as a collection of plug-ins. Each plug-in contains the code that provides some of the product's functionality. The code and other files for a plug-in are installed on the local computer, and get activated automatically as required. A product's plug-ins are grouped together into features. A feature is a unit of separately downloadable and installable functionality.
The fundamentally modular nature of the Eclipse platform makes it easy to install additional features and plug-ins into an Eclipse based product, and to update the product's existing features and plug-ins. You can do this using the Eclipse platform's install and update support found in the Help menu. Eclipse allows you to discover, download, and install features and plug-ins from special web-based Eclipse software sites.
Large Eclipse based products can organize their features into trees starting from the root feature that represents the entire product. This root feature then includes smaller units of functionality all the way down to leaf features that list one or more plug-ins and fragments. The capability to group features hierarchically allows products to be stacked using a 'Russian doll' approach - a large product can build on top of a smaller one by including it and adding more features.
Some included features may be useful add-ons, but are not vital to the proper functioning of the overall product. Feature providers can elect to mark them as optional. Optional features will only be installed if all their required features and plug-ins are available. If not installed right away, optional features can be added at a later date.
The About option on the Help menu provides information about installed features and plug-ins. The Check for Updates and Install New Software commands on the Help menu provide the ability to update existing features, and to find, download, and install new features.