A script element can use the SRC attribute to refer to code stored in an external script library. If a script element refers to an external library and also contains code local to the block defined by the element, the code in the external library is executed before the local code. Windows Internet Explorer 8 or later. In IE8 Standards mode, the value of the SRC attribute depends on the context of the reference to the attribute. When read as a Document Object Model (DOM) attribute, SRC returns an absolute URL. The value specified by the page author is returned when SRC is read as a content attribute, when the page is displayed in an earlier document compatibility mode, or when the page is viewed with an earlier version of the browser. For more information, see Attribute Differences in Internet Explorer 8. In Microsoft Internet Explorer 5 and later, the SRC attribute of the script element can refer to an XML data set if the LANGUAGE attribute is set to XML. The SRC attribute was first available in Microsoft Internet Explorer 3.022. The src property is exposed through the object model as of Microsoft Internet Explorer 4.0.
Microsoft Developer Network: [Windows Internet Explorer API reference Article]