The base element is used to specify a document’s base URL and base target that is used for resolving URI references (relative URLs) within the document.
|Permitted parents||Only permitted to occur once within [``](/html/elements/head).|
<a>) and forms (
<form>) open in a (
target). The default target is _self, resulting in the link opening in the same window as the document currently viewed. This default can be overridden document-wide using
If a document is integrated in an
iframe, it may help to specify
<base target="_parent"> in order to open the links within the iframe in the scope parent document. If _parent or _top are used without the document really being integrated in an hierarchy, expect the behavior of _self.
href= URI, potentially surrounded by spaces
A base element, if it has an href attribute, must come before any other elements in the tree that have attributes defined as taking URLs, except the html element (its manifest attribute isn’t affected by base elements). [Example A]
target= browsing context name or keyword ( _blank, _self, _parent, or _top)
The value of the target attribute is used as the default when hyperlinks and forms in the Document cause navigation.
The example shows a link with the relative destination some-file.html that gets rewritten to http://example.org/deep/some-file.html
<!DOCTYPE html> <html> <head> <title>base element example</title> <base href="http://www.example.org/deep/"> </head> <body> <p>A <a href="some-file.html">relative link</a>.</p> <!-- after resolving the above link equals to --> <p>A <a href="http://www.example.org/deep/some-file.html">relative link</a>.</p> </body> </html>
The example shows that base only affects elements following it
<head> <title>base element example</title> <link href="my-style.css" rel="stylesheet"> <base href="http://example.com"> <link href="my-other-style.css" rel="stylesheet"> <!-- resolves to [current domain and directory]/my-style.css http://example.com/my-other-style.css --> </head>
The example shows how multiple base occurrences are collapsed and ignored
<head> <title>base element example</title> <base href="http://example.com"> <base target="_blank"> <base href="http://webplatform.org" target="_top"> <!-- equals to the single definition: <base href="http://example.com/" target="_blank"> except for Internet Explorer, where only the first element is read: <base href="http://example.com/" target="_self"> --> </head>
- Relative URLs within
<base>don’t work in every browser, resolving a relative base URL was introduced in Firefox 4 and Internet Explorer 10.
<base>only affects elements following it’s declaration.
<base>declarations are illegal, only the first
targetare used, the rest is discarded. Internet Explorer ignores all
<base>instances after the first.
Note Inline SVGs using references like
fill="url(#element-id)" can be a problem in documents using
<base>. The reason is that
url(#element-id) is actually a URL, not a CSS selector. At least Firefox and Chrome are susceptible to this behavior.