Update some comments for the switch to Pest silent rules

Author: mattheww

src/reimplementation/tokenisation/processing/escape_processing.rs

@@ -352,8 +352,8 @@ struct EscapeProcessingParser;
 
 /// Enumeration of the nonterminals used in the escape-processing grammar.
 ///
-/// Some members are nonterminals in the Pest grammar but documented as terminals in the writeup;
-/// see [is_documented_as_terminal] below.
+/// The nonterminals which are documented as terminals don't appear here, because they are defined
+/// using Pest silent rules.
 pub type Nonterminal = Rule;
 
 /// Information from a successful match attempt from the escape-processing grammar

src/reimplementation/tokenisation/tokens_matching.rs

@@ -70,8 +70,8 @@ struct TokenParser;
 /// - the token-kind nonterminals (named in Title_case)
 /// - subsidiary nonterminals     (named in UPPER_CASE)
 ///
-/// Some members are nonterminals in the Pest grammar but documented as terminals in the writeup;
-/// see the is_documented_as_terminal implementation below.
+/// The nonterminals which are documented as terminals don't appear here, because they are defined
+/// using Pest silent rules.
 pub type Nonterminal = Rule;
 
 /// Returns the Pest TOKENS and TOKEN rules to use for the specified Rust edition.