docstr: Modify page content by prepending `foo` config value.
docstr_tok: ["Modify","page","content","by","prepending","`","foo","`","config","value","."]
code: def on_page_content(self, html, **kwargs) -> str:
      """Modify page content by prepending `foo` config value."""
      return f"{self.config.foo} {html}"
  
imports: from __future__ import annotations
  import os
  import unittest
  from typing import TYPE_CHECKING, Optional
  from mkdocs import plugins
  from mkdocs.commands import build
  from mkdocs.config import base
  from mkdocs.config import config_options
  from mkdocs.config.base import ValidationError
  from mkdocs.exceptions import Abort, BuildError, PluginError
  from mkdocs.tests.base import load_config, tempdir
label_desc: Use image node_id 1 for calling the DummyPlugin obj's underlying member method code with example usage: obj.on_page_content(html) and returns: self, str, html