Added Registers to Language Specification

README.md

@@ -26,3 +26,23 @@ graph TD;
     DCE --> CP;
     DCE --> RA;
 ```
+
+## Language Specification
+
+### Registers
+
+A register is a location that can store values of a certain type.
+Registers are defined and bounded to the context of a single function.
+The first assignment of the register to a value (possibly, as a function parameter)
+defines the register type, and the type of the register cannot be changed
+afterwards. A register type can be any valid type, and the size of the register
+(in bits) is unbounded.
+
+Unlike in other, machine specific, assembly languages, the number of available
+registers are not bounded by USM, and their names can be any sequence of non
+whitespace[^1] unicode characters, prefixed by `%`.
+
+[^1]: A unicode whitespace character is one that has the ["WSpace=Y" property](https://en.wikipedia.org/wiki/Whitespace_character#Unicode). For reference, see [Go's unicode.IsSpace standard function](https://pkg.go.dev/unicode#IsSpace).
+
+Registers are not necessarily stored in memory, and thus can't be directly
+dereferenced.