Add the made-for-the-occasion markdown-underline plugin.

user/plugins/markdown-underline/CHANGELOG.md

+# v0.1.0
+## 03/20/2019
+
+1. [](#new)
+    * Convert double underscore inline blocks to underline.

user/plugins/markdown-underline/LICENSE

+The MIT License (MIT)
+
+Copyright (c) 2019 Shady Oryx
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

user/plugins/markdown-underline/README.md

+# Markdown Underline Plugin
+
+Overrides the default behavior to convert double underscore `__` inline blocks to underline `<u>` instead of `<strong>`.
+
+**Use with caution, as underlining makes text harder to read.**
+
+> If you don't think so, please be thankful for your great sight and ortholexia.
+
+Anyways, it's just another tag for your CSS to tinker with, you don't have to underline.
+
+The **Markdown Underline** Plugin is for [Grav CMS](http://github.com/getgrav/grav). Use __double underscore__ create `<u>` tags.
+
+## Installation
+
+Installing the Markdown Underline plugin can be done in one of two ways. The GPM (Grav Package Manager) installation method enables you to quickly and easily install the plugin with a simple terminal command, while the manual method enables you to do so via a zip file.
+
+### GPM Installation (Preferred)
+
+!! NOT SUBMITTED YET
+
+The simplest way to install this plugin is via the [Grav Package Manager (GPM)](http://learn.getgrav.org/advanced/grav-gpm) through your system's terminal (also called the command line).  From the root of your Grav install type:
+
+    bin/gpm install markdown-underline
+
+This will install the Markdown Underline plugin into your `/user/plugins` directory within Grav. Its files can be found under `/your/site/grav/user/plugins/markdown-underline`.
+
+### Manual Installation
+
+To install this plugin, just download the zip version of this repository and unzip it under `/your/site/grav/user/plugins`. Then, rename the folder to `markdown-underline`. You can find these files on [GitHub](https://github.com/goutte/grav-plugin-markdown-underline) or via [GetGrav.org](http://getgrav.org/downloads/plugins#extras).
+
+You should now have all the plugin files under
+
+    /your/site/grav/user/plugins/markdown-underline
+	
+> NOTE: This plugin is a modular component for Grav which requires [Grav](http://github.com/getgrav/grav) and the [Error](https://github.com/getgrav/grav-plugin-error) and [Problems](https://github.com/getgrav/grav-plugin-problems) to operate.
+
+### Admin Plugin
+
+If you use the admin plugin, you can install directly through the admin plugin by browsing the `Plugins` tab and clicking on the `Add` button.
+
+## Configuration
+
+Before configuring this plugin, you should copy the `user/plugins/markdown-underline/markdown-underline.yaml` to `user/config/plugins/markdown-underline.yaml` and only edit that copy.
+
+Here is the default configuration and an explanation of available options:
+
+```yaml
+enabled: true
+```
+
+Note that if you use the admin plugin, a file with your configuration, and named markdown-underline.yaml will be saved in the `user/config/plugins/` folder once the configuration is saved in the admin.
+
+## Usage
+
+    This will be __underlined text__.
+
+yields
+
+    This will be <u>underlined text</u>.
+
+## Future
+
+- Perhaps evolve into a plugin that allows individual overriding of `*`, `**`, `_`, `__` etc.
\ No newline at end of file

user/plugins/markdown-underline/blueprints.yaml

+name: Markdown Underline
+version: 0.1.0
+description: Use `__double underscore__` to create `<u>` tags.
+icon: plug
+author:
+  name: Shady Oryx
+  email: antoine@goutenoir.com
+homepage: https://github.com/Goutte/grav-plugin-markdown-underline
+demo: https://courses.m3p2.ljbac.com
+keywords: grav, plugin, markdown, underline, underscores
+bugs: https://github.com/goutte/grav-plugin-markdown-underline/issues
+docs: https://github.com/goutte/grav-plugin-markdown-underline/blob/develop/README.md
+license: MIT
+
+form:
+  validation: strict
+  fields:
+    enabled:
+      type: toggle
+      label: PLUGIN_ADMIN.PLUGIN_STATUS
+      highlight: 1
+      default: 0
+      options:
+        1: PLUGIN_ADMIN.ENABLED
+        0: PLUGIN_ADMIN.DISABLED
+      validate:
+        type: bool

user/plugins/markdown-underline/languages.yaml

+

user/plugins/markdown-underline/markdown-underline.php

+<?php
+namespace Grav\Plugin;
+
+use Grav\Common\Plugin;
+use RocketTheme\Toolbox\Event\Event;
+
+/**
+ * __some text__ => <u>some text</u>
+ *
+ * Use with caution, as underlining makes text harder to read.
+ * If you don't think so, please be thankful for your great sight and ortholexia.
+ *
+ * Not sure how this will fare with multibyte strings. Probably badly.
+ * Try mb_strlen ?
+ *
+ * Class MarkdownUnderlinePlugin
+ * @package Grav\Plugin
+ */
+class MarkdownUnderlinePlugin extends Plugin
+{
+    /**
+     * @return array
+     *
+     * The getSubscribedEvents() gives the core a list of events
+     *     that the plugin wants to listen to. The key of each
+     *     array section is the event that the plugin listens to
+     *     and the value (in the form of an array) contains the
+     *     callable (or function) as well as the priority. The
+     *     higher the number the higher the priority.
+     */
+    public static function getSubscribedEvents()
+    {
+        return [
+            'onPluginsInitialized' => ['onPluginsInitialized', 0]
+        ];
+    }
+
+    /**
+     * Initialize the plugin
+     */
+    public function onPluginsInitialized()
+    {
+        // Don't proceed if we are in the admin plugin
+        // This check is legacy, and is perhaps not useful?
+        if ($this->isAdmin()) {
+            return;
+        }
+
+        // Enable the main event we are interested in
+        $this->enable([
+            'onMarkdownInitialized' => ['onMarkdownInitialized', 0],
+        ]);
+    }
+
+    public function onMarkdownInitialized(Event $event)
+    {
+        $markdown = $event['markdown'];
+
+        // Add our parser right before the Emphasis one.
+        // See vendor/erusev/parsedown/Parsedown.php#L977
+        $markdown->addInlineType('_', 'Underline', 0);
+
+        $inlineUnderline = function($Excerpt)
+        {
+            if (strlen($Excerpt['text']) < 5) {
+                return;
+            }
+
+            $marker = $Excerpt['text'][0];
+
+            if ($marker !== '_') {
+                return;
+            }
+
+            if ( ! preg_match($this->StrongRegex[$marker], $Excerpt['text'], $matches)) {
+                return;
+            }
+
+            return array(
+                'extent' => strlen($matches[0]),
+                'element' => array(
+                    'name' => 'u',
+                    'handler' => 'line',
+                    'text' => $matches[1],
+                ),
+            );
+        };
+
+        $markdown->inlineUnderline = $inlineUnderline->bindTo($markdown, $markdown);
+    }
+
+}

user/plugins/markdown-underline/markdown-underline.yaml

+enabled: true
+