René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"[ENH]: Parser errors should mention that commands do not exist","articleBody":"### Problem\n\nI recently hit a parser error after upgrading `matplotlib` from 3.4.2 to 3.7.2 in our build:\r\n\r\n```\r\n\\sum_{i=0}^\\infty x_i * \\frac{3}{4} \\binom{3}{4} \\stackrel{3}{4} * \\sqrt[3]{x}\r\n                                                 ^\r\nParseFatalException: Expected token, found '\\'  (at char 49), (line:1, col:50)\r\n```\r\n\r\nAfter digging through a few rabbit holes (e.g., reverting from `pyparsing` 3.1.x to 3.0.9), it turns out that `stackrel` had been deprecated all the way back in 3.1.0.\n\n### Proposed solution\n\nIt would be nice if, instead of an error like this, it says something like '`stackrel` is not a recognized command\". Even better would be to have the `stackrel` deprecation bring up a warning/error at this point.","author":{"url":"https://github.com/mathstuf","@type":"Person","name":"mathstuf"},"datePublished":"2023-09-11T00:32:29.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/26732/matplotlib/issues/26732"}