{
    "html": [
        {
            "name": "title",
            "type": "div",
            "html": [
                {
                    "type": "h1",
                    "html": "Adjunto"
                }
            ]
        },
        {
            "name": "description",
            "caption": "Descripción",
            "class": "input-large",
            "type": "text"
        },
        {
            "name": "pages",
            "caption": "No. páginas",
            "class": "input-large",
            "type": "text"
        },
        {
            "name": "document_type",
            "caption": "TD",
            "class": "input-xlarge",
            "type": "select",
            "options": [
                {
                    "html": "tipo1",
                    "value": "Tipo 2"
                },
                {
                    "html": "tipo1",
                    "value": "Tipo 3"
                }
            ]
        },
        {
            "name": "attachment",
            "caption": "Archivo(s) adjuntos",
            "type": "attachment"
        }
    ]
}
{
    "html": [
        {
            "name": "title",
            "type": "div",
            "html": [
                {
                    "type": "h1",
                    "html": "Adjunto"
                }
            ]
        },
        {
            "name": "description",
            "caption": "Descripción",
            "class": "input-large",
            "type": "text"
        },
        {
            "name": "pages",
            "caption": "No. páginas",
            "class": "input-large",
            "type": "number",
            "validations" : {
              "min" : "1"
            }
        },
        {
            "name": "document_type",
            "caption": "TD",
            "class": "input-xlarge",
            "type": "select",
            "options": [
                {
                    "html": "tipo1",
                    "value": "Tipo 2"
                },
                {
                    "html": "tipo1",
                    "value": "Tipo 3"
                }
            ]
        },
        {
            "name": "attachment",
            "caption": "Archivo(s) adjuntos",
            "type": "attachment"
        }
    ]
}
Change type to pages and add validation min 0
Change type to pages and add validation min 0
