add semicolon as an expression separator

Author: dr-orlovsky

content/design.md

@@ -123,6 +123,8 @@ In Cation, data types, values and functions are all first-class citizens, such t
 expressions.
 
 Expressions are made of named entities, composed together according to the compatibility rules using functions.
+Expressions are separated either with a line feed character (U+000A), or with a semicolon `;` if put on one line one
+after the other.
 
 
 ## Language syntax

content/reference.md

@@ -436,6 +436,9 @@ instantiated using a shorthand [range expressions](#range-expressions).
 
 ### Expressions
 
+Expressions are separated either with a line feed character (U+000A), or with a semicolon `;` if put on one line one
+after the other.
+
 #### Lambda expressions
 
 Lambda expressions have two forms: [operator](#lambda-operator) and [specifier](#lambda-specifier).