src

track - Address of the track (.vtt file). Must be a valid URL. This attribute must be defined. source - Required for <audio> and <video>, address of the media resource. The value of this attribute is ignored when the <source> element is placed inside a <picture> element. video - The URL of the video to embed. This is optional; you may instead use the <source> element within the video block to specify the video to embed. audio - The URL of the audio to embed. This is subject to HTTP access controls. This is optional; you may instead use the <source> element within the audio block to specify the audio to embed. img - The image URL. This attribute is mandatory for the <img> element. On browsers supporting srcset, src is treated like a candidate image with a pixel density descriptor 1x unless an image with this pixel density descriptor is already defined in srcset, or unless srcset contains 'w' descriptors. input - If the value of the type attribute is image, this attribute specifies a URI for the location of an image to display on the graphical submit button, otherwise it is ignored. iframe - The URL of the page to embed. Use 'about:blank' for empty pages that conform to Same-Origin Policy. embed - The URL of the resource being embedded. script - This attribute specifies the URI of an external script; this can be used as an alternative to embedding a script directly within a document. If a script element has a src attribute specified, it should not have a script embedded inside its tags.