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HTML is good for debugging, but is unsuitable for application use.
Specify the format parameter to change the output format.
To see the non HTML representation of the JSON format, set format=json.
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{
    "query": {
        "namespaces": {
            "-2": {
                "id": -2,
                "case": "first-letter",
                "*": "Media",
                "canonical": "Media"
            },
            "-1": {
                "id": -1,
                "case": "first-letter",
                "*": "Special",
                "canonical": "Special"
            },
            "0": {
                "id": 0,
                "case": "first-letter",
                "*": "",
                "content": ""
            },
            "1": {
                "id": 1,
                "case": "first-letter",
                "*": "Talk",
                "subpages": "",
                "canonical": "Talk"
            },
            "2": {
                "id": 2,
                "case": "first-letter",
                "*": "User",
                "subpages": "",
                "canonical": "User"
            },
            "3": {
                "id": 3,
                "case": "first-letter",
                "*": "User talk",
                "subpages": "",
                "canonical": "User talk"
            },
            "4": {
                "id": 4,
                "case": "first-letter",
                "*": "TheMind",
                "canonical": "Project"
            },
            "5": {
                "id": 5,
                "case": "first-letter",
                "*": "TheMind talk",
                "subpages": "",
                "canonical": "Project talk"
            },
            "6": {
                "id": 6,
                "case": "first-letter",
                "*": "File",
                "canonical": "File"
            },
            "7": {
                "id": 7,
                "case": "first-letter",
                "*": "File talk",
                "subpages": "",
                "canonical": "File talk"
            },
            "8": {
                "id": 8,
                "case": "first-letter",
                "*": "MediaWiki",
                "subpages": "",
                "canonical": "MediaWiki"
            },
            "9": {
                "id": 9,
                "case": "first-letter",
                "*": "MediaWiki talk",
                "subpages": "",
                "canonical": "MediaWiki talk"
            },
            "10": {
                "id": 10,
                "case": "first-letter",
                "*": "Template",
                "canonical": "Template"
            },
            "11": {
                "id": 11,
                "case": "first-letter",
                "*": "Template talk",
                "subpages": "",
                "canonical": "Template talk"
            },
            "12": {
                "id": 12,
                "case": "first-letter",
                "*": "Help",
                "canonical": "Help"
            },
            "13": {
                "id": 13,
                "case": "first-letter",
                "*": "Help talk",
                "subpages": "",
                "canonical": "Help talk"
            },
            "14": {
                "id": 14,
                "case": "first-letter",
                "*": "Category",
                "canonical": "Category"
            },
            "15": {
                "id": 15,
                "case": "first-letter",
                "*": "Category talk",
                "subpages": "",
                "canonical": "Category talk"
            }
        }
    }
}