[Commentor] LC-329 Ian Jacobs [Working Group decision] The text already reads: "Avoiding pixel and absolute measures allows the browser to adapt content to fit the display." [Commentor reply] yes [Comment] 
* Adding more rationale: "To enable flexible display, use relative units (e.g., "em") rather than absolute units (e.g., pixels) when specifying dimensions (e.g., shapes or font sizes) in formats such as markup languages and style sheets."