diff --git a/boost.js b/boost.js
deleted file mode 100644
index 81a86f2..0000000
--- a/boost.js
+++ /dev/null
@@ -1,88 +0,0 @@
-/*
-    Copyright (c) 2023 Vinnie Falco (vinnie.falco@gmail.com)
-
-    Distributed under the Boost Software License, Version 1.0. (See accompanying
-    file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
-
-    Official repository: https://github.com/boostorg/antora
-*/
-
-'use strict'
-
-const fs = require('node:fs');
-const path = require('node:path');
-
-
-/*
-    This extension allows every asciidoc attribute
-    specified in the playbook or the command line
-    to become a variable in the playbook using the
-    syntax ${var}.
-*/
-class Ext {
-    static register() {
-        new Ext(this)
-    }
-
-    constructor(ctx) {
-        ;(this.ctx = ctx)
-        .on('contextStarted', this.contextStarted.bind(this))
-    }
-
-    doReplace1(elem, pat, sub) {
-        if (Array.isArray(elem)) {
-            for(var i = 0; i < elem.length; i++)
-                if (typeof elem[i] != "string")
-                    this.doReplace1(elem[i], pat, sub)
-                else
-                    elem[i] = elem[i].replaceAll(pat, sub)
-        } else if (typeof elem == 'object') {
-            for (let key in elem)
-                if (typeof elem[key] != "string")
-                    this.doReplace1(elem[key], pat, sub)
-                else
-                    elem[key] = elem[key].replaceAll(pat, sub)
-        }
-    }
-
-    doReplace(playbook) {
-        for (const [key, value] of Object.entries(playbook.asciidoc.attributes)) {
-            var pat = "${" + key + "}"
-            this.doReplace1(playbook.site, pat, value)
-            this.doReplace1(playbook.urls, pat, value)
-            this.doReplace1(playbook.content, pat, value)
-            this.doReplace1(playbook.output, pat, value)
-            this.doReplace1(playbook.ui, pat, value)
-        }
-    }
-
-    contextStarted({playbook}) {
-        let branch = playbook.asciidoc.attributes['page-boost-branch'];
-
-        if(! branch )
-            throw new Error("Missing required attribute: asciidoc.attributes.page-boost-branch");
-
-        if( branch === "master" || branch === "develop") {
-            playbook.content.tags = ""
-            playbook.content.branches = branch
-        } else {
-            playbook.content.tags = "boost-" + branch
-            playbook.content.branches = null // disable branches
-            playbook.urls.latestVersionSegment = "" // disable tag in URL
-        }
-
-        const cwd = process.cwd();
-        const sources = playbook.content.sources;
-        for (let i = 0; i < sources.length; i++) {
-            const source = sources[i];
-            const antoraYmlPath = path.join(cwd, source.startPath, 'antora.yml');
-            if (fs.existsSync(antoraYmlPath)) {
-                source.url = '.';
-            }
-        }
-
-        this.doReplace(playbook);
-    }
-}
-
-module.exports = Ext
diff --git a/build.sh b/build.sh
index f07ef64..cb711c8 100755
--- a/build.sh
+++ b/build.sh
@@ -2,12 +2,6 @@
 
 if command -v git >/dev/null && git rev-parse --is-inside-work-tree >/dev/null 2>&1; then
   branch=$(git rev-parse --abbrev-ref HEAD)
-else
-  branch="develop"
-fi
-
-if [ "$branch" != "master" ] && [ "$branch" != "develop" ]; then
-  branch="develop"
 fi
 
 ./sitedoc.sh "$branch"
diff --git a/extensions/boost.js b/extensions/boost.js
new file mode 100644
index 0000000..20322e0
--- /dev/null
+++ b/extensions/boost.js
@@ -0,0 +1,142 @@
+/*
+    Copyright (c) 2023 Vinnie Falco (vinnie.falco@gmail.com)
+    Copyright (c) 2023 Alan de Freitas (alandefreitas@gmail.com)
+
+    Distributed under the Boost Software License, Version 1.0. (See accompanying
+    file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+    Official repository: https://github.com/boostorg/antora
+*/
+
+'use strict'
+
+const fs = require('node:fs');
+const path = require('node:path');
+const process = require("process");
+const {execSync} = require('child_process');
+
+/*
+    This extension allows every asciidoc attribute
+    specified in the playbook or the command line
+    to become a variable in the playbook using the
+    syntax ${var}.
+*/
+class BoostPlaybookPatterns {
+    static register() {
+        new BoostPlaybookPatterns(this)
+    }
+
+    constructor(ctx) {
+        ;(this.ctx = ctx)
+            .on('contextStarted', this.contextStarted.bind(this))
+    }
+
+    /**
+     * Recursively replaces all occurrences of a pattern with a substitution string
+     * in an object or array of strings.
+     *
+     * @param {Array|Object} obj - The object or array to modify.
+     * @param {string|RegExp} pattern - The pattern to search for.
+     * @param {string} replacement - The replacement string.
+     * @returns {void}
+     */
+    replaceAll(obj, pattern, replacement) {
+        if (Array.isArray(obj)) {
+            obj.forEach((val, i) => {
+                if (typeof val === "string") obj[i] = val.replaceAll(pattern, replacement);
+                else if (typeof val === "object") this.replaceAll(val, pattern, replacement);
+            });
+        } else if (typeof obj === "object" && obj !== null) {
+            Object.entries(obj).forEach(([key, val]) => {
+                if (typeof val === "string") obj[key] = val.replaceAll(pattern, replacement);
+                else if (typeof val === "object") this.replaceAll(val, pattern, replacement);
+            });
+        }
+    }
+
+    /**
+     * Sets page attributes on the playbook's `asciidoc` object based on the current Git branch and commit.
+     * Also sets the `branches` and `tags` properties of the playbook's `content` object, and optionally
+     * modifies the playbook's `urls` object.
+     *
+     * @param {object} playbook - The playbook object to modify.
+     */
+    setPageAttributes(playbook) {
+        let branch = playbook.asciidoc.attributes['page-boost-branch'];
+        if (!branch)
+            try {
+                branch = execSync('git rev-parse --abbrev-ref HEAD').toString().trim();
+            } catch (error) {
+                branch = 'develop'
+            }
+        playbook.asciidoc.attributes['page-boost-branch'] = branch
+        playbook.content.branches = branch
+
+        let commit_id = playbook.asciidoc.attributes['page-commit-id'];
+        if (!commit_id)
+            try {
+                commit_id = execSync('git rev-parse HEAD').toString().trim().substring(0, 7);
+                playbook.asciidoc.attributes['page-commit-id'] = commit_id
+            } catch (error) {
+                playbook.asciidoc.attributes['page-commit-id'] = undefined
+            }
+
+        if (branch in ["master", "develop"]) {
+            playbook.content.tags = ""
+        } else {
+            playbook.content.tags = "boost-" + branch
+            playbook.urls.latestVersionSegment = "" // disable tag in URL
+        }
+    }
+
+    /**
+     * Sets the `url` property of each source in the playbook's content object
+     * to `'.'` if an `antora.yml` file exists in the source's directory.
+     *
+     * @param {object} playbook - The playbook object to modify.
+     */
+    setContentSourceURLs(playbook) {
+        const cwd = process.cwd();
+        const sources = playbook.content.sources;
+        for (let i = 0; i < sources.length; i++) {
+            const source = sources[i];
+            const antoraYmlPath = path.join(cwd, source.startPath, 'antora.yml');
+            if (fs.existsSync(antoraYmlPath)) {
+                source.url = '.';
+            }
+        }
+    }
+
+    /**
+     * Recursively replaces all occurrences of attribute placeholders in a playbook
+     * with their corresponding attribute values.
+     *
+     * @param {Object} playbook - The playbook to modify.
+     * @returns {void}
+     */
+    replacePatterns(playbook) {
+        for (const [key, value] of Object.entries(playbook.asciidoc.attributes)) {
+            const placeholder = "${" + key + "}";
+            this.replaceAll(playbook.site, placeholder, value);
+            this.replaceAll(playbook.urls, placeholder, value);
+            this.replaceAll(playbook.content, placeholder, value);
+            this.replaceAll(playbook.output, placeholder, value);
+            this.replaceAll(playbook.ui, placeholder, value);
+        }
+    }
+
+    /**
+     * Called when Antora starts processing a playbook. Sets page attributes, content source URLs,
+     * and performs replacements in the playbook's content.
+     *
+     * @param {object} context - An object containing the playbook and other contextual information.
+     * @param {object} context.playbook - The playbook object being processed.
+     */
+    contextStarted({playbook}) {
+        this.setPageAttributes(playbook)
+        this.setContentSourceURLs(playbook);
+        this.replacePatterns(playbook);
+    }
+}
+
+module.exports = BoostPlaybookPatterns
diff --git a/libdoc.sh b/libdoc.sh
index c055822..5a9ab8e 100755
--- a/libdoc.sh
+++ b/libdoc.sh
@@ -62,6 +62,10 @@ else
   commit_id=""
 fi
 
+if [ ! -d "node_modules" ] || [ "$(find package.json -prune -printf '%T@\n' | cut -d . -f 1)" -gt "$(find node_modules -prune -printf '%T@\n' | cut -d . -f 1)" ]; then
+  npm install
+fi
+
 # Run antora command
 while test $# -gt 0; do
   if [ "$1" = "develop" ] || [ "$1" = "master" ]; then
diff --git a/libs.playbook.yml b/libs.playbook.yml
index 67ecb05..cb50a6f 100644
--- a/libs.playbook.yml
+++ b/libs.playbook.yml
@@ -39,19 +39,19 @@ site:
 
 antora:
   extensions:
-    - require: ./boost.js
+    - require: ./extensions/boost.js
     - require: '@antora/lunr-extension'
 
 content:
   sources:
-  - url: https://github.com/vinniefalco/mp11
-    start_path: antora
-  - url: https://github.com/vinniefalco/predef
-    start_path: antora
-  - url: https://github.com/vinniefalco/qvm
-    start_path: antora
-  - url: https://github.com/vinniefalco/unordered
-    start_path: antora
+    - url: https://github.com/vinniefalco/mp11
+      start_path: antora
+    - url: https://github.com/vinniefalco/predef
+      start_path: antora
+    - url: https://github.com/vinniefalco/qvm
+      start_path: antora
+    - url: https://github.com/vinniefalco/unordered
+      start_path: antora
 
 ui:
   bundle:
diff --git a/package-lock.json b/package-lock.json
index 87006b3..46f252d 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -5,7 +5,8 @@
   "packages": {
     "": {
       "dependencies": {
-        "@antora/lunr-extension": "^1.0.0-alpha.8"
+        "@antora/lunr-extension": "^1.0.0-alpha.8",
+        "process": "^0.11.10"
       },
       "devDependencies": {
         "@antora/cli": "3.1.2",
@@ -1827,7 +1828,6 @@
       "version": "0.11.10",
       "resolved": "https://registry.npmjs.org/process/-/process-0.11.10.tgz",
       "integrity": "sha512-cdGef/drWFoydD1JsMzuFf8100nZl+GT+yacc2bEced5f9Rjk4z+WtFUTBu9PhOi9j/jfmBPu0mMEY4wIdAF8A==",
-      "dev": true,
       "engines": {
         "node": ">= 0.6.0"
       }
diff --git a/package.json b/package.json
index c5c301a..a524e2e 100644
--- a/package.json
+++ b/package.json
@@ -4,6 +4,7 @@
     "@antora/site-generator": "3.1.2"
   },
   "dependencies": {
-    "@antora/lunr-extension": "^1.0.0-alpha.8"
+    "@antora/lunr-extension": "^1.0.0-alpha.8",
+    "process": "^0.11.10"
   }
 }
diff --git a/site.playbook.yml b/site.playbook.yml
index 114e40d..a44620c 100644
--- a/site.playbook.yml
+++ b/site.playbook.yml
@@ -17,11 +17,6 @@
 # old-version:  DIGIT+ '_' DIGIT+ '_' DIGIT+
 #
 
-asciidoc:
-  attributes:
-    page-boost-branch: develop
-    page-commit-id: ''
-
 site:
   url: https://antora.cppalliance.org
   title: Boost Site Docs
@@ -29,7 +24,7 @@ site:
 
 antora:
   extensions:
-    - require: ./boost.js
+    - require: ./extensions/boost.js
     - require: '@antora/lunr-extension'
 
 content:
diff --git a/sitedoc.sh b/sitedoc.sh
index a1e6774..6ee2db5 100755
--- a/sitedoc.sh
+++ b/sitedoc.sh
@@ -57,12 +57,10 @@ else
   commit_id=""
 fi
 
-if [ "$1" != "develop" ] && [ "$1" != "master" ]; then
-  echo "invalid argument: '$1'"
-  exit 1
+if [ ! -d "node_modules" ] || [ "$(find package.json -prune -printf '%T@\n' | cut -d . -f 1)" -gt "$(find node_modules -prune -printf '%T@\n' | cut -d . -f 1)" ]; then
+  npm install
 fi
 
-$ANTORA_CMD --fetch \
-  --attribute page-boost-branch="$1" \
-  --attribute page-commit-id="$commit_id" \
-  site.playbook.yml
+echo $ANTORA_CMD --fetch --attribute page-boost-branch="$1" --attribute page-commit-id="$commit_id" site.playbook.yml
+$ANTORA_CMD --fetch --attribute page-boost-branch="$1" --attribute page-commit-id="$commit_id" site.playbook.yml
+