Simple enclosures use the ``Enclosure'' element name and have the following
attributes:
| Attribute | Mandatory | Description |
| url | mandatory | URL of a file represented by this enclosure |
| type | mandatory | Media Type[9] of a data |
| transport | mandatory | Specifies what transport should be used to download content. (see section 3.5 for details) |
| location | optional | Spatial location of enclosure source (see section 3.6 for details) |
| length | optional | Content length of the data |
| rel | optional | This attribute describes the relationship of the enclosing element (``item'', ``atom:entry'' or ``Enclosures'') to the anchor specified by the url attribute. The value of this attribute is a space-separated list of link types. |
| quality | optional | Relative quality factor. Quality factors allow the user or user agent to indicate the relative degree of preference for that media, using the value scale from 0 to 1 (see section 3.4 for details). The default value is 1. |
| Content-ID | optional | Unique identifier of this enclosure (must be unique within ``item'' or ``atom:entry''). (``cid'' URL schema[11] could be used). |
| description | optional | Human-readable brief description of the enclosure contents. |
Simple enclosure is not allowed to have sub-elements.