Begining to code the Ajax action

assets/jquery.ajax.js

@@ -0,0 +1,22 @@
+/*
+ * vim: set ai sw=4 smarttab expandtab: tabstop=8 softtabstop=0
+ *
+ */
+
+jQuery(document).ready( function($){
+  jQuery('.wpdfh_print_checkbox').on("change", function(){
+      $.ajax({
+        url: wpdfh_ajax_object.ajaxurl, // this is the object instantiated in wp_localize_script function
+        type: 'POST',
+        data:{ 
+            action: 'wpdfh_set_print_metadata', // this is the function in your functions.php that will be triggered
+            post_id: $(this).data('post_id'),
+            checked: $(this).prop('checked')
+        },
+        success: function( data ){
+            console.log( data );
+        }
+    });
+    })
+});
+

assets/wp-pdf-helper-admin.css

@@ -0,0 +1,8 @@
+/*
+ * vim: set ai sw=4 smarttab expandtab: tabstop=8 softtabstop=0
+ *
+*/
+
+.column-wp-pdf-helper {
+    width: 50px;
+}

assets/wp-pdf-helper-print.css

@@ -0,0 +1,73 @@
+/*
+ * vim: set ai sw=4 smarttab expandtab: tabstop=8 softtabstop=0
+ *
+*/
+
+video, 
+.attached-videos,
+header, 
+.plyr, 
+.leaflet-marker-photo, 
+.leaflet-top, 
+#wpgpxmaps_downloadfile,
+div:empty,
+nav,
+.wp-block-comments,
+.wp-block-query,
+footer,
+.other-posts,
+.no-print,
+#wpadminbar,
+.skip-link.screen-reader-text
+{
+	display: none !important;
+}
+
+html,
+main,
+#post-content {
+	padding: 0px !important;
+	margin: 0px !important;
+}
+
+.gallery,
+.attached-gpx {
+    page-break-before: auto; /* 'always,' 'avoid,' 'left,' 'inherit,' or 'right' */
+    page-break-after: auto; /* 'always,' 'avoid,' 'left,' 'inherit,' or 'right' */
+    page-break-inside: avoid; /* or 'auto' */
+}
+
+#post-grid {
+	display: flex;
+}
+
+#post-grid-column2 {
+	flex: 70%;
+	padding-left: 10px;
+}
+
+.attached-gpxes {
+	flex: 30%;
+}
+
+.wpgpxmaps_summary {
+	font-size: var(--wp--preset--font-size--small);
+}
+
+.leaflet-control-attribution {
+	font-size: 8px;
+}
+
+.date-prefix {
+	text-transform: capitalize;
+}
+
+.author-line, .author-line > * {
+	margin-bottom: 0px !important;
+	margin-top: 5px !important;
+	font-size: var(--wp--preset--font-size--medium) !important;
+}
+
+.entry-content, wp-block-post-excerpt {
+	text-align: justify;
+

wp-pdf-helper.php

@@ -32,16 +32,36 @@ add_action('manage_media_custom_column', 'manage_custom_columns', 10, 2);
 function manage_custom_columns ($column_key, $post_id) {
     if ($column_key == 'wp-pdf-helper') {
         $checked = (get_post_meta($post_id, 'wpdfh.print', true) == '') ? '' : 'checked'; 
-        echo "<input type='checkbox' name='Print' value='always' $checked />";
-        error_log("PHP: \$column_key: $column_key, \$post_id: $post_id, \$is_printable: $is_printable.", 0);
+        echo "<input type='checkbox' class='wpdfh_print_checkbox' name='Print' data-post_id='$post_id' $checked />";
+//        error_log("PHP: \$column_key: $column_key, \$post_id: $post_id, \$is_printable: $is_printable.", 0);
     }
 }
 
 add_action('admin_enqueue_scripts', 'wpdfh_enqueue_admin_scripts');
 function wpdfh_enqueue_admin_scripts() {
     wp_enqueue_style( 'wpdfh-admin', plugin_dir_url( __FILE__ ) . 'assets/wp-pdf-helper-admin.css'  );
+    wp_register_script(
+            'wpdfh-ajax-admin',
+            plugins_url('assets/jquery.ajax.js', __FILE__),
+            array(),
+            false,
+            true
+            );
+    wp_enqueue_script( 'wpdfh-ajax-admin' );
+    wp_localize_script(
+            'wpdfh-ajax-admin',
+            'wpdfh_ajax_object',
+            array( 'ajaxurl' => admin_url( 'admin-ajax.php' ) )
+            );
 }
 
+add_action( "wp_ajax_wpdfh_set_print_metadata", "wpdfh_set_print_metadata" );
+function wpdfh_set_print_metadata(){
+    error_log("PHP: wpdfh_set_print_metadata", 0);
+    wp_send_json_success();
+}
+
+
 if ( ! array_key_exists('print', $_GET)) {
     return;
 }