Wrap up 0.19.10.

src/ast.rs

@@ -1058,13 +1058,13 @@ impl Stmt {
     }
 }
 
-/// _(INTERNALS)_ A custom syntax definition.
+/// _(INTERNALS)_ A custom syntax expression.
 /// Exported under the `internals` feature only.
 ///
 /// # WARNING
 ///
 /// This type is volatile and may change.
-#[derive(Clone, Hash)]
+#[derive(Debug, Clone, Hash)]
 pub struct CustomExpr {
     /// List of keywords.
     pub keywords: StaticVec<Expr>,
@@ -1074,17 +1074,6 @@ pub struct CustomExpr {
     pub scope_delta: isize,
 }
 
-impl fmt::Debug for CustomExpr {
-    #[inline(always)]
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.write_str("CustomExpr { keywords:")?;
-        fmt::Debug::fmt(&self.keywords, f)?;
-        f.write_str(", tokens:")?;
-        fmt::Debug::fmt(&self.tokens, f)?;
-        f.write_str("}")
-    }
-}
-
 /// _(INTERNALS)_ A binary expression.
 /// Exported under the `internals` feature only.
 ///

src/syntax.rs

@@ -101,6 +101,14 @@ impl Engine {
     /// * `keywords` holds a slice of strings that define the custom syntax.  
     /// * `new_vars` is the number of new variables declared by this custom syntax, or the number of variables removed (if negative).
     /// * `func` is the implementation function.
+    ///
+    /// # Notes
+    ///
+    /// If `new_vars` is positive, then a number of new variables are expected to be pushed into the
+    /// current [`Scope`][crate::Scope].
+    ///
+    /// If `new_vars` is negative, then it is expected that only the top `new_vars` variables in the
+    /// current [`Scope`][crate::Scope] will be _popped_.  Do not randomly remove variables.
     pub fn register_custom_syntax<S: AsRef<str> + Into<ImmutableString>>(
         &mut self,
         keywords: impl AsRef<[S]>,