René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Broken doc build with sphinx 1.8","articleBody":"The doc CI is broken with sphinx 1.8.\r\n\r\nMatplotlib currently defines its own :math: role (based on mathtext rendering + png embedding), but this triggers a warning (fatal on CI for us) with sphinx 1.8 because sphinx now provides its own :math: role by default.\r\n\r\nI removed that definition in #11928, but that doesn't actually help, because ours is slightly different: the mathtext tutorial uses the construct\r\n```\r\n.. role:: math-stix(math)\r\n   :fontset: stix\r\n```\r\nto later be able to use `math-stix` meaning \"render with that fontset, and this causes an error with sphinx 1.8's own math role).\r\n    \r\nI think the long-term solution is to move the mathtext tutorial to use *plots* to display the relevant samples, or to move matplotlib's own :math: role to something like :mplmath:, but in the mean time I can live with a warning about duplicate roles in sphinx's startup.\r\n\r\nIn the meantime we should just pin sphinx\u003c1.8 and restore our own math role.  At least fixing doc-requirements.txt would be nice for 3.0.","author":{"url":"https://github.com/anntzer","@type":"Person","name":"anntzer"},"datePublished":"2018-09-13T13:25:50.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":1},"url":"https://github.com/12108/matplotlib/issues/12108"}