input: Write a python function to fetch and parse HTML content from a given URL, then extract and return all instances of a specified keyword.
  assert fetch_keyword_instances('http://example.net', 'Artificial Intelligence') == ['Artificial Intelligence', 'Artificial Intelligence in various fields']
  assert fetch_keyword_instances('http://example.com', 'Python') == ['Python is a versatile language', 'Learning Python programming']
  assert fetch_keyword_instances('http://example.org', 'Data Science') == ['Data Science and its applications', 'Data Science in healthcare']
output: def fetch_keyword_instances(url, keyword):
      import requests
      from bs4 import BeautifulSoup
      
      # Fetch the HTML content from the URL
      response = requests.get(url)
      html_content = response.text
      
      # Parse the HTML content
      soup = BeautifulSoup(html_content, 'html.parser')
      
      # Extract text and search for instances of the keyword
      instances = []
      for text in soup.stripped_strings:
          if keyword in text:
              instances.append(text)
      
      return instances