tamer: asg::air::meta: Use term "metalinguistic" over "metasyntactic"

The term "metasyntactic" made sense literally---it's a variable in a
metalanguage that expands into a context that is able to contribute to the
language's syntax.  But, the term has a different conventional use in
programming that is misleading.

The term "metalinguistic" is used in mathematics, to describe a metalanguage
or schema atop of a language.  This is more fitting.

DEV-13163

tamer/src/asg/air.rs

@@ -223,7 +223,7 @@ impl ParseState for AirAggregate {
             (PkgTpl(tplst), AirBind(ttok)) => ctx.proxy(tplst, ttok),
             (PkgTpl(tplst), AirDoc(ttok)) => ctx.proxy(tplst, ttok),
 
-            // Metasyntactic variables (metavariables)
+            // Metavariables
             (st @ (PkgTpl(_) | PkgExpr(_)), tok @ AirMeta(..)) => {
                 ctx.ret_or_transfer(st, tok, AirMetaAggregate::new())
             }

tamer/src/asg/air/ir.rs

@@ -670,7 +670,7 @@ sum_ir! {
         /// Subset of [`Air`] tokens for defining [`Tpl`]s.
         ///
         /// Templates serve as containers for objects that reference
-        ///   metasyntactic variables,
+        ///   metavariables,
         ///     defined by [`AirMeta::MetaStart`].
         ///
         /// Template Application
@@ -771,7 +771,7 @@ sum_ir! {
             },
         }
 
-        /// Metasyntactic objects.
+        /// Metalinguistic objects.
         ///
         /// TAME's metalanguage supports the generation of lexemes using
         ///   metavariables.
@@ -781,7 +781,7 @@ sum_ir! {
         ///     yielding objects as if the user had entered the lexemes
         ///     statically.
         ///
-        /// [`AirBind`] is able to utilize metasyntactic variables for
+        /// [`AirBind`] is able to utilize metavariables for
         ///   dynamically generated bindings.
         enum AirMeta {
             /// Begin a metavariable definition.
@@ -805,7 +805,7 @@ sum_ir! {
                 span: span,
                 display: |f| write!(
                     f,
-                    "open definition of metasyntactic variable",
+                    "open definition of metavariable",
                 ),
             },
 
@@ -823,7 +823,7 @@ sum_ir! {
                 span: span,
                 display: |f| write!(
                     f,
-                    "close definition of metasyntactic variable",
+                    "close definition of metavariable",
                 ),
             },
 

tamer/src/asg/air/meta.rs

@@ -28,7 +28,7 @@ use super::{
 };
 use crate::{asg::graph::object::Meta, diagnostic_todo, parse::prelude::*};
 
-/// Metasyntactic variable (metavariable) parser.
+/// Metalinguistic variable (metavariable) parser.
 #[derive(Debug, PartialEq)]
 pub enum AirMetaAggregate {
     /// Ready for the start of a metavariable.

tamer/src/asg/graph/object.rs

@@ -363,7 +363,7 @@ object_gen! {
     /// A template definition.
     Tpl,
 
-    /// Metasyntactic variable (metavariable).
+    /// Metalinguistic variable (metavariable).
     Meta,
 
     /// Documentation.

tamer/src/asg/graph/object/ident.rs

@@ -151,7 +151,7 @@ pub enum Ident {
     ///   result of template expansion---​
     ///     it represents the abstract _idea_ of an identifier,
     ///       to be made concrete at a later time,
-    ///       and is not valid outside of a metasyntactic context.
+    ///       and is not valid outside of a metalinguistic context.
     ///
     /// The associated span represents the location that the identifier
     ///   was defined,

tamer/src/asg/graph/object/meta.rs

@@ -1,4 +1,4 @@
-// Metasyntactic variables represented on the ASG
+// Metalinguistic objects represented on the ASG
 //
 //  Copyright (C) 2014-2023 Ryan Specialty, LLC.
 //
@@ -17,12 +17,18 @@
 //  You should have received a copy of the GNU General Public License
 //  along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
-//! Metasyntactic variables on the ASG.
+//! Metalinguistic objects on the ASG.
 //!
-//! Metasyntactic variables
+//! Metalinguistic variables[^w],
-//!   (sometimes called "metavariables" herein for short)
+//!   called "metavariables" for short,
 //!   have historically been a feature of the template system.
 //! The canonical metavariable is the template parameter.
+//!
+//! [^w]: This term comes from logic; see
+//!         <https://en.wikipedia.org/wiki/Metavariable_(logic)>.
+//!       The term "metasyntactic" was originally used with TAMER,
+//!         but that term generally has a different meaning in programming:
+//!           <https://en.wikipedia.org/wiki/Metasyntactic_variable>.
 
 use super::{prelude::*, Doc, Ident};
 use crate::{
@@ -35,7 +41,7 @@ use crate::{
 };
 use std::fmt::Display;
 
-/// Metasyntactic variable (metavariable).
+/// Metalinguistic variable (metavariable).
 ///
 /// A metavariable is a lexical construct.
 /// Its value is a lexeme that represents an [`Ident`],
@@ -105,10 +111,10 @@ impl Display for Meta {
     fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
         match self {
             Self::Required(_) => {
-                write!(f, "metasyntactic parameter with required value")
+                write!(f, "metalinguistic parameter with required value")
             }
             Self::ConcatList(_) => {
-                write!(f, "metasyntactic concatenation list")
+                write!(f, "metalinguistic concatenation list")
             }
             Self::Lexeme(_, spair) => {
                 write!(f, "lexeme {}", TtQuote::wrap(spair))