diff --git a/README.md b/README.md
index af7cf60..f1d8b27 100644
--- a/README.md
+++ b/README.md
@@ -1,2 +1,16 @@
 # underlined
-Simple Mistune plug-in  that turns `_` tags into `<ul>` instead of `<em>`
+Simple Mistune plug-in  that turns `_` Markdown tags into `<ul>` instead of `<em>` HTML tags
+
+## Use
+
+```Python
+from mistune import Markdown
+from underlined import underlined
+
+md = 'this _text_ is underlined'
+parser = Markdown()
+underlined(parser)
+html = parser(md)
+```
+
+> `this <ul>text</ul> is underlined`
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diff --git a/underlined.py b/underlined.py
new file mode 100644
index 0000000..13fb8b5
--- /dev/null
+++ b/underlined.py
@@ -0,0 +1,54 @@
+__all__ = ['underlined']
+
+import re
+
+UNDERLINED = r'\b_{1,3}(?=[^\s_])'
+UNDERLINED_END_RE = {
+    '_': re.compile(r'(?:(?<!\\)(?:\\\\)*\\_|[^\s_])_(?!_)\b'),
+    '__': re.compile(r'(?:(?<!\\)(?:\\\\)*\\_|[^\s_])__(?!_)\b'),
+    '___': re.compile(r'(?:(?<!\\)(?:\\\\)*\\_|[^\s_])___(?!_)\b'),
+}
+
+def parse_underlined(self, m, state) -> int:
+        pos = m.end()
+        marker = m.group(0)
+        mlen = len(marker)
+        _end_re = UNDERLINED_END_RE[marker]
+        m1 = _end_re.search(state.src, pos)
+        if not m1:
+            state.append_token({'type': 'text', 'raw': marker})
+            return pos
+        end_pos = m1.end()
+        text = state.src[pos:end_pos-mlen]
+        prec_pos = self.precedence_scan(m, state, end_pos)
+        if prec_pos:
+            return prec_pos
+        new_state = state.copy()
+        new_state.src = text
+        new_state.in_underlined = True
+        state.append_token({
+            'type': 'underlined',
+            'children': self.render(new_state),
+        })
+        return end_pos
+
+def render_underlined_mu(self, token, state) -> str:
+        return '`_' + self.render_children(token, state) + '`_'
+
+def render_underlined_html(self, token, state) -> str:
+        return '<u>' + self.render_children(token, state) + '</u>'
+
+def underlined(md):
+    """A mistune plugin to render underlined tags. 
+    Most Markdown parsers render it as emphasis tag.
+
+    Underlined text is surrounded by `_`, `__`, or `___`
+
+    :param md: Markdown instance
+    """
+    md.inline.register('underlined', UNDERLINED, parse_underlined, before='emphasis')
+    if md.renderer: 
+        if md.renderer.NAME == 'html':
+            md.renderer.register('underlined', render_underlined_html)
+        elif md.renderer.NAME == 'micron':
+            md.renderer.register('underlined', render_underlined_mu)
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