const regex = /^[a-z](?:[\.0-9_a-z\xB7\xC0-\xD6\xD8-\xF6\xF8-\u037D\u037F-\u1FFF\u200C\u200D\u203F\u2040\u2070-\u218F\u2C00-\u2FEF\u3001-\uD7FF\uF900-\uFDCF\uFDF0-\uFFFD]|[\uD800-\uDB7F][\uDC00-\uDFFF])*-(?:[\x2D\.0-9_a-z\xB7\xC0-\xD6\xD8-\xF6\xF8-\u037D\u037F-\u1FFF\u200C\u200D\u203F\u2040\u2070-\u218F\u2C00-\u2FEF\u3001-\uD7FF\uF900-\uFDCF\uFDF0-\uFFFD]|[\uD800-\uDB7F][\uDC00-\uDFFF])*$/
const reservedTags = [
  'annotation-xml',
  'color-profile',
  'font-face',
  'font-face-src',
  'font-face-uri',
  'font-face-format',
  'font-face-name',
  'missing-glyph'
]
const notReservedTag = tagName => reservedTags.indexOf(tagName) === -1

export default function isCustomElement(tagName) {
  return regex.test(tagName) &&
    notReservedTag(tagName)
}
