First stab at high-level parsing

Whilethis is simple, it will not work due to embedded XPath in
parameters in some Instapaper directives which are not documented by
FiveFilters. A nominally XPath-aware parser will be required.

lib/SitePattern.php

@@ -0,0 +1,48 @@
+<?php
+/** @license MIT
+ * Copyright 2021, J. King
+ * See LICENSE and AUTHORS files for details */
+
+declare(strict_types=1);
+namespace MensBeam\FullText;
+
+class SitePattern {
+    public function __construct(string $rules) {
+        $lines = preg_split('/\r\n?|\n/', $rules);
+        foreach ($lines as $l => $d) {
+            if (preg_match('/^#|^\s*$/', $d)) {
+                // the line contains no data
+                continue;
+            } elseif (!preg_match('/^([a-z_]+)(?:\(([a-zA-Z0-9\-_]+)\))?:\s*(.+)$/', $d, $m)) {
+                throw new SitePatternException("Malformed data on line ".($l + 1), 1);
+            }
+            [, $directive, $param, $value] = $m;
+            switch ($directive) {
+                case "title":
+                case "body":
+                case "date":
+                case "author":
+                case "strip":
+                case "single_page_link":
+                case "single_page_link_in_feed":
+                case "next_page_link":
+                    # XPath
+                case "strip_id_or_class":
+                case "strip_image_src":
+                case "find_string":
+                    # string
+                case "replace_sring":
+                case "http_header":
+                    # string with param
+                case "tidy":
+                case "prune":
+                case "atodetect_on_failure":
+                    # yes/no boolean
+                case "test_url":
+                    # URL
+                default:
+                    # Unsupported directive
+            }
+        }
+    } 
+}

lib/SitePatternException.php

@@ -0,0 +1,10 @@
+<?php
+/** @license MIT
+ * Copyright 2021, J. King
+ * See LICENSE and AUTHORS files for details */
+
+declare(strict_types=1);
+namespace MensBeam\FullText;
+
+class SitePatternException extends \Exception {
+}