fix: address off-by-one index bug

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---

lib/node_modules/@stdlib/_tools/remark/plugins/remark-svg-equations/examples/fixtures/math_markup.txt

@@ -0,0 +1,22 @@
+# Absolute Value
+
+<section class="intro">
+
+The absolute value is defined as
+
+<!-- <equation class="equation" label="eq:absolute_value" align="center" raw="|x| = \begin{cases} x & \textrm{if}\ x \geq 0 \\ -x & \textrm{if}\ x < 0\end{cases}" alt="Absolute value"> -->
+
+```math
+|x| = \begin{cases} x & \textrm{if}\ x \geq 0 \\ -x & \textrm{if}\ x < 0\end{cases}
+```
+
+<!-- <div class="equation" align="center" data-raw-text="|x| = \begin{cases} x & \textrm{if}\ x \geq 0 \\ -x & \textrm{if}\ x < 0\end{cases}" data-equation="eq:absolute_value">
+    <img src="https://cdn.jsdelivr.net/gh/stdlib-js/stdlib@bb29798906e119fcb2af99e94b60407a270c9b32/lib/node_modules/@stdlib/math/base/special/abs/docs/img/equation_abs.svg" alt="Absolute value">
+    <br>
+</div> -->
+
+<!-- </equation> -->
+
+</section>
+
+<!-- /.intro -->

lib/node_modules/@stdlib/_tools/remark/plugins/remark-svg-equations/examples/math_markup.js

@@ -0,0 +1,42 @@
+/**
+* @license Apache-2.0
+*
+* Copyright (c) 2024 The Stdlib Authors.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+*    http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+'use strict';
+
+var readFileSync = require( 'fs' ).readFileSync;
+var join = require( 'path' ).join;
+var remark = require( 'remark' );
+var insertEquations = require( './../lib' );
+
+// Load a Markdown file...
+var fpath = join( __dirname, 'fixtures/math_markup.txt' );
+var opts = {
+	'encoding': 'utf8'
+};
+var file = readFileSync( fpath, opts );
+
+// Insert equations:
+remark().use( insertEquations ).process( file, done );
+
+function done( error, out ) {
+	if ( error ) {
+		throw error;
+	}
+	// Output the processed Markdown file:
+	console.log( out.contents );
+}

lib/node_modules/@stdlib/_tools/remark/plugins/remark-svg-equations/lib/transformer.js

@@ -203,7 +203,7 @@ function transformer( tree, file, clbk ) {
 
 			// Note: we don't splice--we simply replace--in order to avoid invalidating the indices of the equation elements in the AST. If we were to remove children, a subsequent resolved equation index would no longer be accurate...
 			parent.children[ i+1 ] = newNode;
-			parent.children[ i+1 ] = {
+			parent.children[ i+2 ] = {
 				'type': 'html',
 				'value': '<!-- -->'
 			};