Docusign API: Is pageNumber tag mandatory

I have been looking at the Docusign API webpages and was wondering if the 'pageNumber' tag of any given 'tabs' child (e.g. signHereTabs, initialHereTabs, textTabs etc.) was mandatory?

If I have the following information to use with the Docusign API, will the 'anchorString' value '[POS_Xn]' be searched for within the entire multipage document OR do I have to specify which page the value exists on (in my case page 4 of 7) by adding the 'pageNumber' tag within the 'signHereTabs' declaration?

To be clear, the value '[POS_Xn]' (of the 'anchorString') is only present once in the document to sign.

{
    "emailSubject": "Please sign attached doc",
    "emailBlurb": "Info to be signed",
    "documents": [
        {
            "documentId": "1",
            "documentBase64": "Base64 string",
            "name": "Testfile1.pdf"
        }
    ],
    "recipients": {
        "signers": [
            {
                "email": "abc@test.net",
                "name": "John Doe",
                "recipientId": "1",
                "routingOrder": "1",
                "tabs": {
                    "signHereTabs": [{
                        "anchorString": "[POS_Xn]",
                        "documentId": "1"
                    }]
                }
             }
        ]
    },
    "status": "sent"
}

The pageNumber property is only required if you are placing your tabs using the xPosition and yPosition properties. If you are using an anchor string to place your tabs there's no need to include the pageNumber property as the tab will be placed at every location where the anchor string appears in the document and every page of the document will be searched for the anchor string.