title: How to add "Align bottom to: parent view" system constraint?
body: <p>Just created a demo single view controller project. Controller view contains collection view, and it contains cell view (orange). Cell view contains a view (selected inside) and I need to align it to bottom of cell view. However, when I select orange view inside cell view, press Ctrl and drag it to cell view I don't see "Align bottom to container view" or similar. There's only "Bottom Space to Container" selection and I'm not sure does it have the same behaviour:</p>
  
  <p><img src="https://i.stack.imgur.com/gfBNv.png" alt="enter image description here"></p>
  
  <p>And if I select "Bottom Space to Container" and don't get desired "Align bottom to parent" system constraint:</p>
  
  <p><img src="https://i.stack.imgur.com/nNI5t.png" alt="enter image description here"></p>
  
  <p>I need to add a new label in existing code base with auto layout, and the label must be positioned next to existing label that has "Align bottom to: parent cell" system constraint:</p>
  
  <p><img src="https://i.stack.imgur.com/xyvL7.png" alt="enter image description here"></p>
  
  <p>There's some setting "Bottom edges" if I select my new label and press align button icon at the bottom. However, this selection is disabled anyways and I assume this is user constraint but I need system constraint "Align bottom to: parent cell". Any suggestions why existing label has this constraint but I can't add a similar one to the new label?</p>
  
  <p><img src="https://i.stack.imgur.com/r1qIV.png" alt="enter image description here"></p>