document_base_url

This option specifies the base URL for all relative URLs in the document. The default value is the directory of the current document. If a value is provided, it must specify a directory (not a document) and must end with a "/". This option also interacts with the relative_urls, remove_script_host, and convert_urls options to determine whether TinyMCE returns relative or absolute URLs. The FAQ contains a thorough description and an example page of working with relative/absolute URLs.

Example of usage of the document_base_url option:

tinymce.init({
        ...
        document_base_url: "http://www.site.com/path1/"
});