title: What are the safe characters for making URLs?
body: <p>I am making a website with articles, and I need the articles to have &quot;friendly&quot; URLs, based on the title.</p>
  <p>For example, if the title of my article is <code>&quot;Article Test&quot;</code>, I would like the URL to be <code>http://www.example.com/articles/article_test</code>.</p>
  <p>However, article titles (as any string) can contain multiple special characters that would not be possible to put literally in my URL. For instance, I know that <code>?</code> or <code>#</code> need to be replaced, but I don't know all the others.</p>
  <p>What characters are permissible in URLs? What is safe to keep?</p>