The provided document is an extensive technical overview of the CSS Values and Units Module Level 4, which defines the foundational system for how all values, units, and mathematical expressions are processed in Cascading Style Sheets. It outlines the core data types like , , and , and details the complex processing pipeline from specified value (what the author wrote) through computed, used, and actual values, emphasizing how relative units are resolved to absolute units (often in canonical px) at specific stages. The text also thoroughly explains absolute and relative units—including expanded font-relative units (like rem, cap, lh) and new viewport-relative units (lvw, svh, dvh)—and describes the syntax and compatibility rules for mathematical functions such as calc(), min(), and clamp(). Furthermore, it addresses how these definitions ensure consistent parsing, animation interpolation, and interaction with scripting APIs like the CSS Typed Object Model across different browser implementations.