CDA is a flexible standard and is unique in that it can be read by the human eye or processed by a machine. This is due to its use of XML language, which also allows the standard to be broken into two different parts. A mandatory free-form portion enables human interpretation of the document, while an optional structured part enables electronic processing (like with an EMR system). Text, images and even multimedia can be included in the document.
A CDA document could be, for example, any of the following: discharge summary, referral, clinical summary, history/physical examination, diagnostic report, prescription, or public health report. In short, any document that might have a signature is a viable document for CDA.