entirely of decimal digits (and possibly underscores) is considered a decimal
integer, even if it starts with a leading <code>0</code>.
</p>

<pre>
0i
0123i         // == 123i for backward-compatibility
0o123i        // == 0o123 * 1i == 83i
0xabci        // == 0xabc * 1i == 2748i
0.i
2.71828i
1.e+0i
6.67428e-11i
1E6i
.25i
.12345E+5i

	PLHA 1234(R1), $0, R3                   // 06000000a86104d2
	PLHZ 1234(R1), $0, R3                   // 06000000a06104d2
	PLQ 1234(R1), $0, R4                    // 04000000e08104d2
	PLWA 1234(R1), $0, R3                   // 04000000a46104d2
	PLWZ 1234567890(R4), $0, R3             // 06004996806402d2
	PLWZ 1234567890(R0), $1, R3             // 06104996806002d2
	PLXSD 1234(R1), $0, V1                  // 04000000a82104d2

		lines(
			"#define A",
			"#ifdef A",
			"#define B 1234",
			"#endif",
			"B",
		),
		"1234.\n",
	},
	{
		"not taken #ifdef",
		lines(
			"#ifdef A",
			"#define B 1234",
			"#endif",
			"B",
		),
		"B.\n",
	},
	{
		"taken #ifdef with else",
		lines(
			"#define A",
			"#ifdef A",
			"#define B 1234",
			"#else",
			"#define B 5678",
			"#endif",