René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"validation of `pivot` in `quiver`","articleBody":"Noted as part of #3907, the inputs on `pivot` for quiver is very permissive and will take 'mid' or 'middle', however it will also work with out exception with _any_ string input (by just silently falling back to 'tail'):\n\n``` python\nX, Y = np.meshgrid(np.linspace(-np.pi, np.pi, 16), np.linspace(-np.pi, np.pi, 16))\nv = np.sin(X)\nu = np.cos(Y)\nplt.quiver(X, Y, u, v)\nplt.quiver(X, Y, u, v, color='b', pivot='ardvaark', alpha=.5)\n```\n\nI propose that a) we validate the input to be in `{'tip', 'tail', 'mid', 'middle'}` and accept but warn anything else down to `tail` for one version before raising.\n","author":{"url":"https://github.com/tacaswell","@type":"Person","name":"tacaswell"},"datePublished":"2014-12-28T01:14:43.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/3951/matplotlib/issues/3951"}