code: function form(context, value, all) {
    var dict = context.data
    var flags = context.flags
    var alternative
  
    value = trim(value)
  
    if (!value) {
      return null
    }
  
    value = normalize(value, context.conversion.in)
  
    if (exact(context, value)) {
      if (!all && flag(flags, 'FORBIDDENWORD', dict[value])) {
        return null
      }
  
      return value
    }
  
    // Try sentence-case if the value is upper-case.
    if (value.toUpperCase() === value) {
      alternative = value.charAt(0) + value.slice(1).toLowerCase()
  
      if (ignore(flags, dict[alternative], all)) {
        return null
      }
  
      if (exact(context, alternative)) {
        return alternative
      }
    }
  
    // Try lower-case.
    alternative = value.toLowerCase()
  
    if (alternative !== value) {
      if (ignore(flags, dict[alternative], all)) {
        return null
      }
  
      if (exact(context, alternative)) {
        return alternative
      }
    }
  
    return null
  }
docs: Find a known form of `value`.