A component platform from the W3C that allows websites to be constructed from standardized building blocks. Web Components comprise Custom Elements, Shadow DOM and HTML Imports and Templates. Custom Elements and Shadow DOM Custom Elements are user-defined components. Shadow DOM is a subtree in a DOM tree (document object model tree) that cannot be influenced by scripts and style sheets. HTML Imports and Templates HTML Imports allows for the inclusion of an HTML document inside another HTML document, and HTML Templates enable HTML code to be used like a separate routine called for when required. See Polymer.