diff --git a/CHANGELOG.md b/CHANGELOG.md
index 58d94f7..6ce0f75 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,10 +2,13 @@
 
 ## 0.3.0
 
-- Add auth loaders i.e. `sqlalchemy.require_auth_base()`, `flask_sqlalchemy`
+- Add SQLAlchemy auth loaders i.e. `sqlalchemy.require_auth_base()`, `flask_sqlalchemy`.
+  What auth loaders do is loading user token and signature into app
+- Implement `UserSigner()`
 - Improve JSON handling in `flask_restx`
-- Add base2048 (i.e. BIP-39) codec
-- Add `split_bits()` and `join_bits()`
+- Add base2048 (i.e. [BIP-39](https://github.com/bitcoin/bips/blob/master/bip-0039.mediawiki)) codec
+- Add `split_bits()`, `join_bits()`, `ltuple()`, `rtuple()`
+- Add `markdown` extensions
 
 ## 0.2.3
 
diff --git a/pyproject.toml b/pyproject.toml
index d452ebd..36540a6 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -44,7 +44,9 @@ flask_sqlalchemy = [
 peewee = [
     "peewee>=3.0.0, <4.0"
 ]
-
+markdown = [
+    "markdown>=3.0.0"
+]
 
 [tool.setuptools.dynamic]
 version = { attr = "suou.__version__" }
diff --git a/src/suou/__init__.py b/src/suou/__init__.py
index 6328936..8b87268 100644
--- a/src/suou/__init__.py
+++ b/src/suou/__init__.py
@@ -25,7 +25,7 @@ from .classtools import Wanted, Incomplete
 from .itertools import makelist, kwargs_prefix, ltuple, rtuple
 from .i18n import I18n, JsonI18n, TomlI18n
 
-__version__ = "0.3.0-dev21"
+__version__ = "0.3.0-dev22"
 
 __all__ = (
     'Siq', 'SiqCache', 'SiqType', 'SiqGen', 'StringCase',
diff --git a/src/suou/bits.py b/src/suou/bits.py
index 8ab2053..0288c0f 100644
--- a/src/suou/bits.py
+++ b/src/suou/bits.py
@@ -50,8 +50,6 @@ def count_ones(n: int) -> int:
 def split_bits(buf: bytes, nbits: int) -> list[int]:
     '''
     Split a bytestring into chunks of equal size, and interpret each chunk as an unsigned integer.
-
-    XXX DOES NOT WORK DO NOT USE!!!!!!!!
     '''
     mem = memoryview(buf)
     chunk_size = nbits // math.gcd(nbits, 8)
diff --git a/src/suou/markdown.py b/src/suou/markdown.py
new file mode 100644
index 0000000..58ce15d
--- /dev/null
+++ b/src/suou/markdown.py
@@ -0,0 +1,89 @@
+"""
+Plugins for markdown.
+
+---
+
+Copyright (c) 2025 Sakuragasaki46.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+See LICENSE for the specific language governing permissions and
+limitations under the License.
+
+This software is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+"""
+
+import re
+import markdown
+from markdown.inlinepatterns import InlineProcessor, SimpleTagInlineProcessor
+import xml.etree.ElementTree as etree
+
+class StrikethroughExtension(markdown.extensions.Extension):
+    """
+    Turn ~~crossed out~~ (with double tilde) text into HTML strikethrough
+
+    well, markdown-strikethrough is a trivial dependency lol
+    """
+    def extendMarkdown(self, md: markdown.Markdown, md_globals=None):
+        postprocessor = StrikethroughPostprocessor(md)
+        md.postprocessors.register(postprocessor, 'strikethrough', 0)
+
+class StrikethroughPostprocessor(markdown.postprocessors.Postprocessor):
+    PATTERN = re.compile(r"~~(((?!~~).)+)~~", re.DOTALL)
+
+    def run(self, html):
+        return re.sub(self.PATTERN, self.convert, html)
+
+    def convert(self, match: re.Match):
+        return '<del>' + match.group(1) + '</del>'
+
+
+class SpoilerExtension(markdown.extensions.Extension):
+    """
+    Add spoiler tags to text, using >!Reddit syntax!<.
+
+    XXX remember to call SpoilerExtension.patch_blockquote_processor()
+    to clear conflicts with the blockquote processor and allow
+    spoiler tags to start at beginning of line.
+    """
+    def extendMarkdown(self, md: markdown.Markdown, md_globals=None):
+        md.inlinePatterns.register(SimpleTagInlineProcessor(r'()>!(.*?)!<', 'span class="spoiler"'), 'spoiler', 14)
+
+    @classmethod
+    def patch_blockquote_processor(cls):
+        """Patch BlockquoteProcessor to make Spoiler prevail over blockquotes."""
+        from markdown.blockprocessors import BlockQuoteProcessor
+        BlockQuoteProcessor.RE = re.compile(r'(^|\n)[ ]{0,3}>(?!!)[ ]?(.*)')
+
+
+class MentionPattern(InlineProcessor):
+    def __init__(self, regex, url_prefix: str):
+        super().__init__(regex)
+        self.url_prefix = url_prefix
+    def handleMatch(self, m, data):
+        el = etree.Element('a')
+        el.attrib['href'] = self.url_prefix + m.group(1)
+        el.text = m.group(0)
+        return el, m.start(0), m.end(0)
+
+class PingExtension(markdown.extensions.Extension):
+    """
+    Convert @mentions into profile links.
+
+    Customizable by passing a dict as mappings= argument, where
+    the key is the first character, and the value is the URL prefix.
+    """
+    mappings: dict[str, str]
+    DEFAULT_MAPPINGS = {'@': '/@'}
+    CHARACTERS = r'[a-zA-Z0-9_-]{2,32}'
+
+    def __init__(self, /, mappings: dict | None = None, **kwargs):
+        super().__init__(**kwargs)
+        self.mappings = mappings or self.DEFAULT_MAPPINGS.copy()
+    def extendMarkdown(self, md: markdown.Markdown, md_globals=None):
+        for at, url_prefix in self.mappings.items():
+            md.inlinePatterns.register(MentionPattern(re.escape(at) + r'(' + self.CHARACTERS + ')', url_prefix), 'ping_mention', 14)
+
+
+__all__ = ('PingExtension', 'SpoilerExtension', 'StrikethroughExtension')