Shortened description and replaced spaces with hyphens in aliases

Author: shaedrich

topics/cst/index.md

@@ -2,9 +2,9 @@
 created_by: 
 display_name: Concrete syntax tree
 released: 
-short_description: A concrete syntax tree is an ordered, rooted tree that represents the syntactic structure of a string according to some context-free grammar.
+short_description: A concrete syntax tree is a low level representation of the parsed source in the structure defined by a grammar description.
 topic: cst
-aliases: parse tree, parsing tree, derivation tree
+aliases: parse-tree, parsing-tree, derivation-tree
 url:
 wikipedia_url: https://en.wikipedia.org/wiki/Parse_tree
 related: ast