title: vim not allowing backspace
body: <p>File <code>foo</code> has text:</p>
  
  <pre><code>This| is a line.
  </code></pre>
  
  <p>If I place the cursor at the <code>|</code>, hop into <code>insert</code> mode, and press <kbd>backspace</kbd>, nothing happens. If I type something, I can delete the things I've typed, but only back to where the insertion began. For example, if I place the cursor at the end of the line, and type <code>word</code>, I can delete <code>word</code> but can't delete the <code>.</code> or anything to the left of it. </p>
  
  <p>This is rather annoying. What <code>vim</code> setting does this?</p>