All descendants of the specified element are searched, but not the element itself. The returned list is live, which means it updates itself with the DOM tree automatically. Therefore, there is no need to call
Element.getElementsByTagName() with the same element and arguments repeatedly if the DOM changes in between calls.
When called on an HTML element in an HTML document,
getElementsByTagName lower-cases the argument before searching for it. This is undesirable when trying to match camel-cased SVG elements (such as
<linearGradient>) in an HTML document. Instead, use
Element.getElementsByTagNameNS(), which preserves the capitalization of the tag name.
Element.getElementsByTagName is similar to
Document.getElementsByTagName(), except that it only searches for elements that are descendants of the specified element.