Do we need to define "user agent" in the spec?

Below is the definition from W3C: A user agent is any software that retrieves and presents Web content for end users or is implemented using Web technologies.
User agents include Web browsers, media players, and plug-ins that help in retrieving, rendering and interacting with Web content.
The family of user agents also includes operating system shells, consumer electronics with Web-widgets, and stand-alone applications or embedded applications whose user interface is implemented as a combination of Web technologies.
https://www.w3.org/WAI/UA/work/wiki/Definition_of_User_Agent

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Best, Kris Kristen James Eberlein Chair, OASIS DITA Technical Committee OASIS Distinguished Contributor Principal consultant, Eberlein Consulting LLC www.eberleinconsulting.com +1 919 622-1501; kriseberlein (skype)