diff --git a/boot.php b/boot.php
index 14c0a88ed..830a636ac 100644
--- a/boot.php
+++ b/boot.php
@@ -25,6 +25,7 @@ use Friendica\Core\Protocol;
 use Friendica\Core\System;
 use Friendica\Database\DBA;
 use Friendica\Model\Contact;
+use Friendica\Model\Term;
 use Friendica\Util\BasePath;
 use Friendica\Util\DateTimeFormat;
 
@@ -171,23 +172,27 @@ define('NOTIFY_SYSTEM',   32768);
 /* @}*/
 
 
-/**
- * @name Term
- *
- * Tag/term types
- * @{
- */
-define('TERM_UNKNOWN',   0);
-define('TERM_HASHTAG',   1);
-define('TERM_MENTION',   2);
-define('TERM_CATEGORY',  3);
-define('TERM_PCATEGORY', 4);
-define('TERM_FILE',      5);
-define('TERM_SAVEDSEARCH', 6);
-define('TERM_CONVERSATION', 7);
+/** @deprecated since 2019.03, use Term::UNKNOWN instead */
+define('TERM_UNKNOWN',   Term::UNKNOWN);
+/** @deprecated since 2019.03, use Term::HASHTAG instead */
+define('TERM_HASHTAG',   Term::HASHTAG);
+/** @deprecated since 2019.03, use Term::MENTION instead */
+define('TERM_MENTION',   Term::MENTION);
+/** @deprecated since 2019.03, use Term::CATEGORY instead */
+define('TERM_CATEGORY',  Term::CATEGORY);
+/** @deprecated since 2019.03, use Term::PCATEGORY instead */
+define('TERM_PCATEGORY', Term::PCATEGORY);
+/** @deprecated since 2019.03, use Term::FILE instead */
+define('TERM_FILE',      Term::FILE);
+/** @deprecated since 2019.03, use Term::SAVEDSEARCH instead */
+define('TERM_SAVEDSEARCH', Term::SAVEDSEARCH);
+/** @deprecated since 2019.03, use Term::CONVERSATION instead */
+define('TERM_CONVERSATION', Term::CONVERSATION);
 
-define('TERM_OBJ_POST',  1);
-define('TERM_OBJ_PHOTO', 2);
+/** @deprecated since 2019.03, use Term::OBJECT_TYPE_POST instead */
+define('TERM_OBJ_POST',  Term::OBJECT_TYPE_POST);
+/** @deprecated since 2019.03, use Term::OBJECT_TYPE_PHOTO instead */
+define('TERM_OBJ_PHOTO', Term::OBJECT_TYPE_PHOTO);
 
 /**
  * @name Namespaces
diff --git a/src/Model/Term.php b/src/Model/Term.php
index 6e3425524..5266627ac 100644
--- a/src/Model/Term.php
+++ b/src/Model/Term.php
@@ -6,32 +6,61 @@ namespace Friendica\Model;
 
 use Friendica\Core\System;
 use Friendica\Database\DBA;
+use Friendica\Util\Strings;
 
 class Term
 {
-	public static function tagTextFromItemId($itemid)
-	{
-		$tag_text = '';
-		$condition = ['otype' => TERM_OBJ_POST, 'oid' => $itemid, 'type' => [TERM_HASHTAG, TERM_MENTION]];
-		$tags = DBA::select('term', [], $condition);
-		while ($tag = DBA::fetch($tags)) {
-			if ($tag_text != '') {
-				$tag_text .= ',';
-			}
+    const UNKNOWN           = 0;
+    const HASHTAG           = 1;
+    const MENTION           = 2;
+    const CATEGORY          = 3;
+    const PCATEGORY         = 4;
+    const FILE              = 5;
+    const SAVEDSEARCH       = 6;
+    const CONVERSATION      = 7;
+    const IMPLICIT_MENTION  = 8;
+    const EXCLUSIVE_MENTION = 9;
 
-			if ($tag['type'] == 1) {
-				$tag_text .= '#';
-			} else {
-				$tag_text .= '@';
-			}
-			$tag_text .= '[url=' . $tag['url'] . ']' . $tag['term'] . '[/url]';
+    const TAG_CHARACTER = [
+    	self::HASHTAG           => '#',
+    	self::MENTION           => '@',
+    	self::IMPLICIT_MENTION  => '%',
+    	self::EXCLUSIVE_MENTION => '!',
+    ];
+
+    const OBJECT_TYPE_POST  = 1;
+    const OBJECT_TYPE_PHOTO = 2;
+
+	/**
+	 * Generates the legacy item.tag field comma-separated BBCode string from an item ID.
+	 * Includes only hashtags, implicit and explicit mentions.
+	 *
+	 * @param int $item_id
+	 * @return string
+	 * @throws \Exception
+	 */
+	public static function tagTextFromItemId($item_id)
+	{
+		$tag_list = [];
+		$tags = self::tagArrayFromItemId($item_id, [self::HASHTAG, self::MENTION, self::IMPLICIT_MENTION]);
+		foreach ($tags as $tag) {
+			$tag_list[] = self::TAG_CHARACTER[$tag['type']] . '[url=' . $tag['url'] . ']' . $tag['term'] . '[/url]';
 		}
-		return $tag_text;
+
+		return implode(',', $tag_list);
 	}
 
-	public static function tagArrayFromItemId($itemid, $type = [TERM_HASHTAG, TERM_MENTION])
+	/**
+	 * Retrieves the terms from the provided type(s) associated with the provided item ID.
+	 *
+	 * @param int       $item_id
+	 * @param int|array $type
+	 * @return array
+	 * @throws \Exception
+	 */
+	public static function tagArrayFromItemId($item_id, $type = [self::HASHTAG, self::MENTION])
 	{
-		$condition = ['otype' => TERM_OBJ_POST, 'oid' => $itemid, 'type' => $type];
+		$condition = ['otype' => self::OBJECT_TYPE_POST, 'oid' => $item_id, 'type' => $type];
 		$tags = DBA::select('term', ['type', 'term', 'url'], $condition);
 		if (!DBA::isResult($tags)) {
 			return [];
@@ -40,22 +69,39 @@ class Term
 		return DBA::toArray($tags);
 	}
 
-	public static function fileTextFromItemId($itemid)
+	/**
+	 * Generates the legacy item.file field string from an item ID.
+	 * Includes only file and category terms.
+	 *
+	 * @param int $item_id
+	 * @return string
+	 * @throws \Exception
+	 */
+	public static function fileTextFromItemId($item_id)
 	{
 		$file_text = '';
-		$condition = ['otype' => TERM_OBJ_POST, 'oid' => $itemid, 'type' => [TERM_FILE, TERM_CATEGORY]];
-		$tags = DBA::select('term', [], $condition);
-		while ($tag = DBA::fetch($tags)) {
-			if ($tag['type'] == TERM_CATEGORY) {
+		$tags = self::tagArrayFromItemId($item_id, [self::FILE, self::CATEGORY]);
+		foreach ($tags as $tag) {
+			if ($tag['type'] == self::CATEGORY) {
 				$file_text .= '<' . $tag['term'] . '>';
 			} else {
 				$file_text .= '[' . $tag['term'] . ']';
 			}
 		}
+
 		return $file_text;
 	}
 
-	public static function insertFromTagFieldByItemId($itemid, $tags)
+	/**
+	 * Inserts new terms for the provided item ID based on the legacy item.tag field BBCode content.
+	 * Deletes all previous tag terms for the same item ID.
+	 * Sets both the item.mention and thread.mentions field flags if a mention concerning the item UID is found.
+	 *
+	 * @param int    $item_id
+	 * @param string $tag_str
+	 * @throws \Friendica\Network\HTTPException\InternalServerErrorException
+	 */
+	public static function insertFromTagFieldByItemId($item_id, $tag_str)
 	{
 		$profile_base = System::baseUrl();
 		$profile_data = parse_url($profile_base);
@@ -64,32 +110,32 @@ class Term
 		$profile_base_diaspora = $profile_data['host'] . $profile_path . '/u/';
 
 		$fields = ['guid', 'uid', 'id', 'edited', 'deleted', 'created', 'received', 'title', 'body', 'parent'];
-		$message = Item::selectFirst($fields, ['id' => $itemid]);
-		if (!DBA::isResult($message)) {
+		$item = Item::selectFirst($fields, ['id' => $item_id]);
+		if (!DBA::isResult($item)) {
 			return;
 		}
 
-		$message['tag'] = $tags;
+		$item['tag'] = $tag_str;
 
 		// Clean up all tags
-		self::deleteByItemId($itemid);
+		self::deleteByItemId($item_id);
 
-		if ($message['deleted']) {
+		if ($item['deleted']) {
 			return;
 		}
 
-		$taglist = explode(',', $message['tag']);
+		$taglist = explode(',', $item['tag']);
 
 		$tags_string = '';
 		foreach ($taglist as $tag) {
-			if ((substr(trim($tag), 0, 1) == '#') || (substr(trim($tag), 0, 1) == '@') || (substr(trim($tag), 0, 1) == '!')) {
+			if (Strings::startsWith($tag, self::TAG_CHARACTER)) {
 				$tags_string .= ' ' . trim($tag);
 			} else {
 				$tags_string .= ' #' . trim($tag);
 			}
 		}
 
-		$data = ' ' . $message['title'] . ' ' . $message['body'] . ' ' . $tags_string . ' ';
+		$data = ' ' . $item['title'] . ' ' . $item['body'] . ' ' . $tags_string . ' ';
 
 		// ignore anything in a code block
 		$data = preg_replace('/\[code\](.*?)\[\/code\]/sm', '', $data);
@@ -103,11 +149,15 @@ class Term
 			}
 		}
 
-		$pattern = '/\W([\#@!])\[url\=(.*?)\](.*?)\[\/url\]/ism';
+		$pattern = '/\W([\#@!%])\[url\=(.*?)\](.*?)\[\/url\]/ism';
 		if (preg_match_all($pattern, $data, $matches, PREG_SET_ORDER)) {
 			foreach ($matches as $match) {
 
-				if (($match[1] == '@') || ($match[1] == '!')) {
+				if (in_array($match[1], [
+					self::TAG_CHARACTER[self::MENTION],
+					self::TAG_CHARACTER[self::IMPLICIT_MENTION],
+					self::TAG_CHARACTER[self::EXCLUSIVE_MENTION]
+				])) {
 					$contact = Contact::getDetailsByURL($match[2], 0);
 					if (!empty($contact['addr'])) {
 						$match[3] = $contact['addr'];
@@ -118,12 +168,12 @@ class Term
 					}
 				}
 
-				$tags[$match[1] . trim($match[3], ',.:;[]/\"?!')] = $match[2];
+				$tags[$match[2]] = $match[1] . trim($match[3], ',.:;[]/\"?!');
 			}
 		}
 
-		foreach ($tags as $tag => $link) {
-			if (substr(trim($tag), 0, 1) == '#') {
+		foreach ($tags as $link => $tag) {
+			if (self::isType($tag, self::HASHTAG)) {
 				// try to ignore #039 or #1 or anything like that
 				if (ctype_digit(substr(trim($tag), 1))) {
 					continue;
@@ -134,11 +184,15 @@ class Term
 					continue;
 				}
 
-				$type = TERM_HASHTAG;
+				$type = self::HASHTAG;
 				$term = substr($tag, 1);
 				$link = '';
-			} elseif ((substr(trim($tag), 0, 1) == '@') || (substr(trim($tag), 0, 1) == '!')) {
-				$type = TERM_MENTION;
+			} elseif (self::isType($tag, self::MENTION, self::EXCLUSIVE_MENTION, self::IMPLICIT_MENTION)) {
+				if (self::isType($tag, self::MENTION, self::EXCLUSIVE_MENTION)) {
+					$type = self::MENTION;
+				} else {
+					$type = self::IMPLICIT_MENTION;
+				}
 
 				$contact = Contact::getDetailsByURL($link, 0);
 				if (!empty($contact['name'])) {
@@ -147,43 +201,49 @@ class Term
 					$term = substr($tag, 1);
 				}
 			} else { // This shouldn't happen
-				$type = TERM_HASHTAG;
+				$type = self::HASHTAG;
 				$term = $tag;
 				$link = '';
 			}
 
-			if (DBA::exists('term', ['uid' => $message['uid'], 'otype' => TERM_OBJ_POST, 'oid' => $itemid, 'term' => $term])) {
+			if (DBA::exists('term', ['uid' => $item['uid'], 'otype' => self::OBJECT_TYPE_POST, 'oid' => $item_id, 'term' => $term, 'type' => $type])) {
 				continue;
 			}
 
-			if ($message['uid'] == 0) {
+			if ($item['uid'] == 0) {
 				$global = true;
-				DBA::update('term', ['global' => true], ['otype' => TERM_OBJ_POST, 'guid' => $message['guid']]);
+				DBA::update('term', ['global' => true], ['otype' => self::OBJECT_TYPE_POST, 'guid' => $item['guid']]);
 			} else {
-				$global = DBA::exists('term', ['uid' => 0, 'otype' => TERM_OBJ_POST, 'guid' => $message['guid']]);
+				$global = DBA::exists('term', ['uid' => 0, 'otype' => self::OBJECT_TYPE_POST, 'guid' => $item['guid']]);
 			}
 
 			DBA::insert('term', [
-				'uid'      => $message['uid'],
-				'oid'      => $itemid,
-				'otype'    => TERM_OBJ_POST,
+				'uid'      => $item['uid'],
+				'oid'      => $item_id,
+				'otype'    => self::OBJECT_TYPE_POST,
 				'type'     => $type,
 				'term'     => $term,
 				'url'      => $link,
-				'guid'     => $message['guid'],
-				'created'  => $message['created'],
-				'received' => $message['received'],
+				'guid'     => $item['guid'],
+				'created'  => $item['created'],
+				'received' => $item['received'],
 				'global'   => $global
 			]);
 
 			// Search for mentions
-			if (((substr($tag, 0, 1) == '@') || (substr($tag, 0, 1) == '!')) && (strpos($link, $profile_base_friendica) || strpos($link, $profile_base_diaspora))) {
-				$users = q("SELECT `uid` FROM `contact` WHERE self AND (`url` = '%s' OR `nurl` = '%s')", $link, $link);
+			if (self::isType($tag, self::MENTION, self::EXCLUSIVE_MENTION)
+				&& (
+					strpos($link, $profile_base_friendica) !== false
+					|| strpos($link, $profile_base_diaspora) !== false
+				)
+			) {
+				$users_stmt = DBA::p("SELECT `uid` FROM `contact` WHERE self AND (`url` = ? OR `nurl` = ?)", $link, $link);
+				$users = DBA::toArray($users_stmt);
 				foreach ($users AS $user) {
-					if ($user['uid'] == $message['uid']) {
-						/// @todo This function is called frim Item::update - so we mustn't call that function here
-						DBA::update('item', ['mention' => true], ['id' => $itemid]);
-						DBA::update('thread', ['mention' => true], ['iid' => $message['parent']]);
+					if ($user['uid'] == $item['uid']) {
+						/// @todo This function is called from Item::update - so we mustn't call that function here
+						DBA::update('item', ['mention' => true], ['id' => $item_id]);
+						DBA::update('thread', ['mention' => true], ['iid' => $item['parent']]);
 					}
 				}
 			}
@@ -191,20 +251,23 @@ class Term
 	}
 
 	/**
-	 * @param integer $itemid item id
+	 * Inserts new terms for the provided item ID based on the legacy item.file field BBCode content.
+	 * Deletes all previous file terms for the same item ID.
+	 *
+	 * @param integer $item_id item id
 	 * @param         $files
 	 * @return void
 	 * @throws \Exception
 	 */
-	public static function insertFromFileFieldByItemId($itemid, $files)
+	public static function insertFromFileFieldByItemId($item_id, $files)
 	{
-		$message = Item::selectFirst(['uid', 'deleted'], ['id' => $itemid]);
+		$message = Item::selectFirst(['uid', 'deleted'], ['id' => $item_id]);
 		if (!DBA::isResult($message)) {
 			return;
 		}
 
 		// Clean up all tags
-		DBA::delete('term', ['otype' => TERM_OBJ_POST, 'oid' => $itemid, 'type' => [TERM_FILE, TERM_CATEGORY]]);
+		DBA::delete('term', ['otype' => self::OBJECT_TYPE_POST, 'oid' => $item_id, 'type' => [self::FILE, self::CATEGORY]]);
 
 		if ($message["deleted"]) {
 			return;
@@ -216,9 +279,9 @@ class Term
 			foreach ($files[1] as $file) {
 				DBA::insert('term', [
 					'uid' => $message["uid"],
-					'oid' => $itemid,
-					'otype' => TERM_OBJ_POST,
-					'type' => TERM_FILE,
+					'oid' => $item_id,
+					'otype' => self::OBJECT_TYPE_POST,
+					'type' => self::FILE,
 					'term' => $file
 				]);
 			}
@@ -228,9 +291,9 @@ class Term
 			foreach ($files[1] as $file) {
 				DBA::insert('term', [
 					'uid' => $message["uid"],
-					'oid' => $itemid,
-					'otype' => TERM_OBJ_POST,
-					'type' => TERM_CATEGORY,
+					'oid' => $item_id,
+					'otype' => self::OBJECT_TYPE_POST,
+					'type' => self::CATEGORY,
 					'term' => $file
 				]);
 			}
@@ -252,6 +315,7 @@ class Term
 			'tags' => [],
 			'hashtags' => [],
 			'mentions' => [],
+			'implicit_mentions' => [],
 		];
 
 		$searchpath = System::baseUrl() . "/search?tag=";
@@ -259,10 +323,9 @@ class Term
 		$taglist = DBA::select(
 			'term',
 			['type', 'term', 'url'],
-			["`otype` = ? AND `oid` = ? AND `type` IN (?, ?)", TERM_OBJ_POST, $item['id'], TERM_HASHTAG, TERM_MENTION],
+			['otype' => self::OBJECT_TYPE_POST, 'oid' => $item['id'], 'type' => [self::HASHTAG, self::MENTION, self::IMPLICIT_MENTION]],
 			['order' => ['tid']]
 		);
-
 		while ($tag = DBA::fetch($taglist)) {
 			if ($tag['url'] == '') {
 				$tag['url'] = $searchpath . rawurlencode($tag['term']);
@@ -270,25 +333,25 @@ class Term
 
 			$orig_tag = $tag['url'];
 
-			$author = ['uid' => 0, 'id' => $item['author-id'],
-				'network' => $item['author-network'], 'url' => $item['author-link']];
+			$prefix = self::TAG_CHARACTER[$tag['type']];
+			switch($tag['type']) {
+				case self::HASHTAG:
+					if ($orig_tag != $tag['url']) {
+						$item['body'] = str_replace($orig_tag, $tag['url'], $item['body']);
+					}
 
-			$prefix = '';
-			if ($tag['type'] == TERM_HASHTAG) {
-				$tag['url'] = Contact::magicLinkByContact($author, $tag['url']);
-				if ($orig_tag != $tag['url']) {
-					$item['body'] = str_replace($orig_tag, $tag['url'], $item['body']);
-				}
-
-				$return['hashtags'][] = '#<a href="' . $tag['url'] . '" target="_blank">' . $tag['term'] . '</a>';
-				$prefix = '#';
-			} elseif ($tag['type'] == TERM_MENTION) {
-				$tag['url'] = Contact::magicLink($tag['url']);
-				$return['mentions'][] = '@<a href="' . $tag['url'] . '" target="_blank">' . $tag['term'] . '</a>';
-				$prefix = '@';
+					$return['hashtags'][] = $prefix . '<a href="' . $tag['url'] . '" target="_blank">' . $tag['term'] . '</a>';
+					$return['tags'][] = $prefix . '<a href="' . $tag['url'] . '" target="_blank">' . $tag['term'] . '</a>';
+					break;
+				case self::MENTION:
+					$tag['url'] = Contact::magicLink($tag['url']);
+					$return['mentions'][] = $prefix . '<a href="' . $tag['url'] . '" target="_blank">' . $tag['term'] . '</a>';
+					$return['tags'][] = $prefix . '<a href="' . $tag['url'] . '" target="_blank">' . $tag['term'] . '</a>';
+					break;
+				case self::IMPLICIT_MENTION:
+					$return['implicit_mentions'][] = $prefix . $tag['term'];
+					break;
 			}
-
-			$return['tags'][] = $prefix . '<a href="' . $tag['url'] . '" target="_blank">' . $tag['term'] . '</a>';
 		}
 		DBA::close($taglist);
 
@@ -296,20 +359,38 @@ class Term
 	}
 
 	/**
-	 * Delete all tags from an item
+	 * Delete tags of the specific type(s) from an item
 	 *
-	 * @param int itemid - choose from which item the tags will be removed
-	 * @param array $type
+	 * @param int       $item_id
+	 * @param int|array $type
 	 * @throws \Exception
 	 */
-	public static function deleteByItemId($itemid, $type = [TERM_HASHTAG, TERM_MENTION])
+	public static function deleteByItemId($item_id, $type = [self::HASHTAG, self::MENTION, self::IMPLICIT_MENTION])
 	{
-		if (empty($itemid)) {
+		if (empty($item_id)) {
 			return;
 		}
 
 		// Clean up all tags
-		DBA::delete('term', ['otype' => TERM_OBJ_POST, 'oid' => $itemid, 'type' => $type]);
+		DBA::delete('term', ['otype' => self::OBJECT_TYPE_POST, 'oid' => $item_id, 'type' => $type]);
+	}
 
+	/**
+	 * Check if the provided tag is of one of the provided term types.
+	 *
+	 * @param string $tag
+	 * @param int    ...$types
+	 * @return bool
+	 */
+	public static function isType($tag, ...$types)
+	{
+		$tag_chars = [];
+		foreach ($types as $type) {
+			if (isset(self::TAG_CHARACTER[$type])) {
+				$tag_chars[] = self::TAG_CHARACTER[$type];
+			}
+		}
+
+		return Strings::startsWith($tag, $tag_chars);
 	}
 }
diff --git a/src/Util/Strings.php b/src/Util/Strings.php
index 0c63749c8..55751d8d8 100644
--- a/src/Util/Strings.php
+++ b/src/Util/Strings.php
@@ -331,4 +331,19 @@ class Strings
 
 		return $uri;
 	}
+
+
+	/**
+	 * Check if the trimmed provided string is starting with one of the provided characters
+	 *
+	 * @param string $string
+	 * @param array  $chars
+	 * @return bool
+	 */
+	public static function startsWith($string, array $chars)
+	{
+		$return = in_array(substr(trim($string), 0, 1), $chars);
+
+		return $return;
+	}
 }