ctype_alpha

<?php     public function toBeAlpha(string $message = ''): self

    {

        Assert::assertTrue(ctype_alpha((string) $this->value), $message);



        return $this;

    }

<?php         }



        $splitDriveLetter = function ($path) {

            return (\strlen($path) > 2 && ':' === $path[1] && '/' === $path[2] && ctype_alpha($path[0]))

                ? [substr($path, 2), strtoupper($path[0])]

                : [$path, null];

        };

<?php     public function isAbsolutePath(string $file)

    {

        return '' !== $file && (strspn($file, '/\\', 0, 1)

            || (\strlen($file) > 3 && ctype_alpha($file[0])

                && ':' === $file[1]

                && strspn($file, '/\\', 2, 1)

            )