Update syntax-intro.md

src/syntax-intro.md

@@ -1,13 +1,20 @@
 # Syntax and the AST
 
 Working directly with source code is very inconvenient and error-prone. Thus,
-before we do anything else, we convert raw source code into an AST. It turns
+before we do anything else, we convert raw source code into an [Abstract Syntax
-out that doing even this involves a lot of work, including lexing, parsing,
+Tree (`AST`)][`AST`]. It turns out that doing even this involves a lot of work,
-macro expansion, name resolution, conditional compilation, feature-gate
+including [lexing, parsing], [`macro` expansion], [name resolution], conditional
-checking, and validation of the AST. In this chapter, we take a look at all
+compilation, [feature-gate checking], and [validation] of the [`AST`]. In this chapter,
-of these steps.
+we take a look at all of these steps.
 
 Notably, there isn't always a clean ordering between these tasks. For example,
-macro expansion relies on name resolution to resolve the names of macros and
+`macro` expansion relies on name resolution to resolve the names of `macro`s and
-imports. And parsing requires macro expansion, which in turn may require
+imports. And parsing requires `macro` expansion, which in turn may require
-parsing the output of the macro.
+parsing the output of the `macro`.
+
+[`AST`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_parse/index.html
+[`macro` expansion]: ./macro-expansion.md
+[feature-gate checking]: ./feature-gate-ck.md
+[lexing, parsing]: ./lexing-parsing.md
+[name resolution]: ./name-resolution.md
+[validation]: ./ast-validation.md