function assertUnitNameIsValid (name) {
    for (let i = 0; i < name.length; i++) {
      c = name.charAt(i)

      if (i === 0 && !Unit.isValidAlpha(c)) { throw new Error('Invalid unit name (must begin with alpha character): "' + name + '"') }

      if (i > 0 && !(Unit.isValidAlpha(c) ||
        isDigit(c))) { throw new Error('Invalid unit name (only alphanumeric characters are allowed): "' + name + '"') }
    }
  }
Checks if a character is a valid latin letter (upper or lower case).
Note that this function can be overridden, for example to allow support of other alphabets.
@memberof Unit
@param {string} c Tested character
@return {boolean} true if the character is a latin letter