XHTML (.xhtml)

def is_xhtml(file_path: str) -> bool:
    """Check if file is a valid XHTML by magic bytes."""
    signature = bytes([0x3C, 0x68, 0x74, 0x6D, 0x6C, 0x20, 0x78, 0x6D, 0x6C, 0x6E, 0x73, 0x3D])
    with open(file_path, "rb") as f:
        return f.read(12) == signature

function isXHTML(buffer: Buffer): boolean {
  const signature = Buffer.from([0x3C, 0x68, 0x74, 0x6D, 0x6C, 0x20, 0x78, 0x6D, 0x6C, 0x6E, 0x73, 0x3D]);
  return buffer.subarray(0, 12).equals(signature);
}

func IsXHTML(data []byte) bool {
    signature := []byte{0x3C, 0x68, 0x74, 0x6D, 0x6C, 0x20, 0x78, 0x6D, 0x6C, 0x6E, 0x73, 0x3D}
    if len(data) < 12 {
        return false
    }
    return bytes.Equal(data[:12], signature)
}