diff --git a/libc/include/dirent.h b/libc/include/dirent.h
index ece25d1e..0ab7d654 100644
--- a/libc/include/dirent.h
+++ b/libc/include/dirent.h
@@ -107,7 +107,7 @@ int scandir(const char*, struct dirent***, int (*)(const struct dirent*),
 int versionsort(const struct dirent**, const struct dirent**);
 int versionsort_r(const struct dirent**, const struct dirent**, void*);
 
-#if defined(_SORTIX_SOURCE)
+#if __USE_SORTIX
 void dregister(DIR* dir);
 void dunregister(DIR* dir);
 DIR* dnewdir(void);
diff --git a/libc/include/error.h b/libc/include/error.h
index 42b608f3..c8d1c655 100644
--- a/libc/include/error.h
+++ b/libc/include/error.h
@@ -31,10 +31,8 @@ __BEGIN_DECLS
 
 void gnu_error(int status, int errnum, const char* format, ...)
 	__attribute__((__format__(__printf__, 3, 4)));
-#if __SORTIX_STDLIB_REDIRECTS
 void error(int status, int errnum, const char* format, ...) __asm__ ("gnu_error")
 	__attribute__((__format__(__printf__, 3, 4)));
-#endif
 
 __END_DECLS
 
diff --git a/libc/include/features.h b/libc/include/features.h
index 63c0de7c..93e3eeaa 100644
--- a/libc/include/features.h
+++ b/libc/include/features.h
@@ -1,6 +1,6 @@
 /*******************************************************************************
 
-    Copyright(C) Jonas 'Sortie' Termansen 2011, 2012, 2013.
+    Copyright(C) Jonas 'Sortie' Termansen 2011, 2012, 2013, 2014.
 
     This file is part of the Sortix C Library.
 
@@ -49,24 +49,158 @@
 	 ((gcc_major) < __GNUC__))
 
 /* Sortix system components implicitly use the native API. */
-#if defined(__is_sortix_system_component)
+#if defined(__is_sortix_system_component) && !defined(_SORTIX_SOURCE)
 #define _SORTIX_SOURCE 1
 #endif
 
-/* By default, assume the source is compiled using the native API. */
-#if !defined(_SORTIX_SOURCE) && \
-    !defined(_POSIX_SOURCE) && !defined(_POSIX_C_SOURCE) && \
-    !defined(_BSD_SOURCE) && \
-    !defined(_SVID_SOURCE) && \
-    !defined(_XOPEN_SOURCE) && !defined(_XOPEN_SOURCE_EXTENDED) && \
-    !defined(_GNU_SOURCE) && \
-    1
+/* These macros are used internally by the standard library to decide which
+   symbols are provided by the standard library headers. They are always defined
+   and have a value of zero if the feature is not activated. */
+#undef __USE_C
+#undef __USE_POSIX
+#undef __USE_XOPEN
+#undef __USE_SORTIX
+
+/* Determine if all symbols should be visible in an effort to be as compatible
+   as possible, even if the Sortix API doesn't have them in these places. */
+#if defined(_ALL_SOURCE)
+	#if !defined(_C11_SOURCE)
+		#define _C11_SOURCE
+	#endif
+	#if !defined(_POSIX_C_SOURCE)
+		#define _POSIX_C_SOURCE 200809L
+	#endif
+	#if !defined(_XOPEN_SOURCE)
+		#define _XOPEN_SOURCE 700
+	#endif
+	#if !defined(_SORTIX_SOURCE)
+		#define _SORTIX_SOURCE 1
+		#define __IMPLICIT_SORTIX_SOURCE
+	#endif
+#endif
+
+/* Default to the native API if no other base feature macros is defined. */
+#if !defined(__STRICT_ANSI__) && \
+    !defined(_ANSI_SOURCE) && \
+    !defined(_ISOC99_SOURCE) && \
+    !defined(_ISOC11_SOURCE) && \
+    !defined(_XOPEN_SOURCE) && \
+    !defined(_POSIX_SOURCE) && \
+    !defined(_POSIX_C_SOURCE) && \
+    !defined(_ALL_SOURCE) && \
+    !defined(_SORTIX_SOURCE) && \
+    !defined(_DEFAULT_SOURCE)
+	#define _DEFAULT_SOURCE 1
+#endif
+
+/* Use the Sortix API if the default API was requested. */
+#if defined(_DEFAULT_SOURCE) && !defined(_SORTIX_SOURCE)
 	#define _SORTIX_SOURCE 1
+	#define __IMPLICIT_SORTIX_SOURCE
+#endif
+
+/* Particular XSI revisions imply certain POSIX revisions. */
+#if defined(_XOPEN_SOURCE)
+	#if 700 <= _XOPEN_SOURCE - 0
+		#undef _POSIX_C_SOURCE
+		#define _POSIX_C_SOURCE 200809L
+	#elif 600 <= _XOPEN_SOURCE - 0
+		#undef _POSIX_C_SOURCE
+		#define _POSIX_C_SOURCE 200112L
+	#elif 520 <= _XOPEN_SOURCE - 0
+		#undef _POSIX_C_SOURCE
+		#define _POSIX_C_SOURCE 199506L
+	#elif 500 <= _XOPEN_SOURCE - 0
+		#undef _POSIX_C_SOURCE
+		#define _POSIX_C_SOURCE 199506L
+	#endif
+#endif
+
+/* C89 is always visible. */
+#define __USE_C 1989
+
+/* Determine if C90 Amendment 1:1995 is visible. */
+#if defined(__STDC_VERSION__) && 199409L <= __STDC_VERSION__
+	#undef __USE_C
+	#define __USE_C 1995
+#endif
+
+/* Determine if C99 is visible. */
+#if defined(_ISOC99_SOURCE) || \
+    (defined(__STDC_VERSION__) && 199901L <= __STDC_VERSION__) || \
+    (defined(__cplusplus) && 201103L <= __cplusplus)
+	#undef __USE_C
+	#define __USE_C 1999
+#endif
+
+/* Determine if C11 is visible. */
+#if defined(_ISOC11_SOURCE) || \
+    (defined(__STDC_VERSION__) && 201112L <= __STDC_VERSION__)
+	#undef __USE_C
+	#define __USE_C 2011
+#endif
+
+/* Determine which revision of XSI is used. */
+#if defined(_XOPEN_SOURCE)
+	#if 700 <= _XOPEN_SOURCE - 0
+		#define __USE_XOPEN 700
+	#elif 600 <= _XOPEN_SOURCE - 0
+		#define __USE_XOPEN 600
+	#elif 520 <= _XOPEN_SOURCE - 0
+		#define __USE_XOPEN 520
+	#elif 500 <= _XOPEN_SOURCE - 0
+		#define __USE_XOPEN 500
+	#elif 1 == _XOPEN_SOURCE_EXTENDED - 0
+		#define __USE_XOPEN 420
+	#elif 4 <= _XOPEN_VERSION - 0
+		#define __USE_XOPEN 400
+	#else
+		#define __USE_XOPEN 300
+	#endif
+#else
+	#define __USE_XOPEN 0
+#endif
+
+/* Determine which revision of POSIX is used. */
+#ifdef _POSIX_C_SOURCE
+	#if 200809L <= _POSIX_C_SOURCE - 0
+		#define __USE_POSIX 200809L
+	#elif 200112L <= _POSIX_C_SOURCE - 0
+		#define __USE_POSIX 200112L
+	#elif 199506L <= _POSIX_C_SOURCE - 0
+		#define __USE_POSIX 199506L
+	#elif 199309L <= _POSIX_C_SOURCE - 0
+		#define __USE_POSIX 199309L
+	#elif 2 <= _POSIX_C_SOURCE - 0
+		#define __USE_POSIX 199209L
+	#else
+		#define __USE_POSIX 199009L
+	#endif
+#elif defined(_POSIX_SOURCE)
+	#define __USE_POSIX 198808L
+#else
+	#define __USE_POSIX 0
+#endif
+
+/* Upgrade the visible C revision in accordance with the used POSIX revision. */
+#if 200112L <= __USE_POSIX && __USE_C < 1999
+	#undef __USE_C
+	#define __USE_C 1999
+#elif 0 < __USE_POSIX && __USE_C < 1990
+	#undef __USE_C
+	#define __USE_C 1990
+#endif
+
+/* Determine whether the Sortix API is visible. */
+#if defined(_SORTIX_SOURCE)
+#define __USE_SORTIX 1
+#else
+#define __USE_SORTIX 0
 #endif
 
 /* Whether to override some "standard" functions with Sortix alternatives. */
 #if !defined(__SORTIX_STDLIB_REDIRECTS)
-	#if defined(_SORTIX_SOURCE)
+	#if __USE_SORTIX && !defined(__IMPLICIT_SORTIX_SOURCE)
 		#define __SORTIX_STDLIB_REDIRECTS 1
 	#else
 		#define __SORTIX_STDLIB_REDIRECTS 0
@@ -86,8 +220,10 @@
 /* Provide the full <stdint.h> in all system components. */
 #if defined(__is_sortix_system_component)
 #undef __STDC_CONSTANT_MACROS
+#undef __STDC_FORMAT_MACROS
 #undef __STDC_LIMIT_MACROS
 #define __STDC_CONSTANT_MACROS
+#define __STDC_FORMAT_MACROS
 #define __STDC_LIMIT_MACROS
 #endif
 
diff --git a/libc/include/locale.h b/libc/include/locale.h
index e14c4cc9..e2612178 100644
--- a/libc/include/locale.h
+++ b/libc/include/locale.h
@@ -69,7 +69,7 @@ struct lconv
 #define LC_NUM_CATEGORIES LC_ALL
 
 const char* sortix_setlocale(int category, const char* locale);
-#if defined(_SORTIX_SOURCE) && __SORTIX_STDLIB_REDIRECTS
+#if __USE_SORTIX && __SORTIX_STDLIB_REDIRECTS
 const char* setlocale(int category, const char* locale) __asm__ ("sortix_setlocale");
 #else
 char* setlocale(int category, const char* locale);
diff --git a/libc/include/stdio.h b/libc/include/stdio.h
index 86fdbd26..3be9ae97 100644
--- a/libc/include/stdio.h
+++ b/libc/include/stdio.h
@@ -214,7 +214,7 @@ char* ctermid(char* s);
 FILE* open_memstream(char** bufp, size_t* sizep);
 #endif
 
-#if defined(_SORTIX_SOURCE)
+#if __USE_SORTIX
 
 #define FILE_MODE_READ (1 << 0)
 #define FILE_MODE_WRITE (1 << 1)
@@ -264,7 +264,7 @@ int fpipe(FILE* pipes[2]);
 int fparsemode(const char*);
 #endif
 
-#if defined(_SORTIX_SOURCE) || defined(_WANT_SORTIX_VPRINTF_CALLBACK)
+#if __USE_SORTIX
 size_t vprintf_callback(size_t (*callback)(void*, const char*, size_t),
                         void* user,
                         const char* __restrict format,
diff --git a/libc/include/string.h b/libc/include/string.h
index 6ba2dd24..e556148c 100644
--- a/libc/include/string.h
+++ b/libc/include/string.h
@@ -64,6 +64,7 @@ char* stpncpy(char* __restrict, const char* __restrict, size_t);
 int strcasecmp(const char* a, const char* b);
 char* strcat(char* __restrict, const char* __restrict);
 char* strchr(const char*, int);
+char* strchrnul(const char* str, int c);
 int strcmp(const char*, const char*);
 int strcoll(const char*, const char*);
 int strcoll_l(const char*, const char*, locale_t);
@@ -90,16 +91,12 @@ int strverscmp(const char*, const char*);
 size_t strxfrm(char* __restrict, const char* __restrict, size_t);
 size_t strxfrm_l(char* __restrict, const char* __restrict, size_t, locale_t);
 
-#if defined(_SORTIX_SOURCE) || defined(_GNU_SOURCE)
-char* strchrnul(const char* str, int c);
-#endif
-
-#if defined(_SORTIX_SOURCE)
+#if __USE_SORTIX
 const char* sortix_strerror(int errnum);
 const char* sortix_strerror_l(int, locale_t);
 const char* sortix_strsignal(int signum);
 #endif
-#if defined(_SOURCE_SOURCE) && __SORTIX_STDLIB_REDIRECTS
+#if __USE_SORTIX && __SORTIX_STDLIB_REDIRECTS
 const char* strerror(int errnum) __asm__ ("sortix_strerror");
 const char* strerror_l(int, locale_t) __asm__ ("sortix_strerror_l");
 const char* strsignal(int signum) __asm__ ("sortix_strsignal");
diff --git a/libc/include/time.h b/libc/include/time.h
index ea01bdd8..4df95b2e 100644
--- a/libc/include/time.h
+++ b/libc/include/time.h
@@ -88,7 +88,7 @@ struct tm
 __END_DECLS
 #include <sortix/timespec.h>
 #include <sortix/itimerspec.h>
-#if defined(_SORTIX_SOURCE)
+#if __USE_SORTIX
 #include <sortix/tmns.h>
 #endif
 __BEGIN_DECLS
@@ -144,7 +144,7 @@ void tzset(void);
 /* TODO: This is some _MISC_SOURCE thing according to GNU, but I like it. */
 time_t timegm(struct tm*);
 
-#if defined(_SORTIX_SOURCE)
+#if __USE_SORTIX
 int clock_gettimeres(clockid_t, struct timespec*, struct timespec*);
 int clock_settimeres(clockid_t, const struct timespec*, const struct timespec*);
 int timens(struct tmns* tmns);
diff --git a/libc/include/unistd.h b/libc/include/unistd.h
index 9627e4fe..6ccfd5fa 100644
--- a/libc/include/unistd.h
+++ b/libc/include/unistd.h
@@ -33,7 +33,7 @@
 #include <sys/__/types.h>
 #include <__/stdint.h>
 
-#if defined(_SORTIX_SOURCE)
+#if __USE_SORTIX
 #include <stdarg.h>
 #include <stdint.h>
 #include <sortix/exit.h>
@@ -50,8 +50,6 @@ __END_DECLS
 #include <sortix/seek.h>
 #include <sortix/unistd.h>
 
-#define _SORTIX_ALWAYS_SBRK
-
 __BEGIN_DECLS
 
 /* Currently just say we support the newest POSIX. */
@@ -379,6 +377,7 @@ ssize_t readlink(const char* __restrict, char* __restrict, size_t);
 ssize_t readlinkat(int, const char* __restrict, char* __restrict, size_t);
 ssize_t read(int, void*, size_t);
 int rmdir(const char*);
+void* sbrk(__intptr_t increment);
 int setegid(gid_t);
 int seteuid(uid_t);
 int setgid(gid_t);
@@ -399,7 +398,7 @@ int unlinkat(int, const char*, int);
 int unlink(const char*);
 ssize_t write(int, const void*, size_t);
 
-#if defined(_SORTIX_SOURCE)
+#if __USE_SORTIX
 int alarmns(const struct timespec* delay, struct timespec* odelay);
 int execvpe(const char*, char* const [], char* const []);
 int exit_thread(int, int, const struct exit_thread*);
@@ -410,12 +409,9 @@ pid_t tfork(int flags, struct tfork* regs);
 size_t writeall(int fd, const void* buf, size_t count);
 size_t writeleast(int fd, const void* buf, size_t least, size_t max);
 #endif
-#if defined(_SORTIX_SOURCE) || defined(_SORTIX_ALWAYS_SBRK)
-void* sbrk(__intptr_t increment);
-#endif
 
 /* For compatibility with POSIX, declare getopt(3) here. */
-#if !defined(_SORTIX_SOURCE)
+#if __USE_POSIX
 /* These declarations are repeated in <getopt.h>. */
 #ifndef __getopt_unistd_shared_declared
 #define __getopt_unistd_shared_declared
diff --git a/libm/include/fenv.h b/libm/include/fenv.h
index 80a3a0e2..52b3a74d 100644
--- a/libm/include/fenv.h
+++ b/libm/include/fenv.h
@@ -51,13 +51,13 @@ int feholdexcept(fenv_t *);
 int fesetenv(const fenv_t *);
 int feupdateenv(const fenv_t *);
 
-#if defined(_NETBSD_SOURCE) || defined(_GNU_SOURCE) || defined(_SORTIX_SOURCE)
+#if __USE_SORTIX
 
 int feenableexcept(int mask);
 int fedisableexcept(int mask);
 int fegetexcept(void);
 
-#endif /* _NETBDS_SOURCE || _GNU_SOURCE */
+#endif /* __USE_SORTIX */
 
 __END_DECLS
 
diff --git a/libm/include/math.h b/libm/include/math.h
index d781c23d..2a08e1a6 100644
--- a/libm/include/math.h
+++ b/libm/include/math.h
@@ -55,7 +55,7 @@ __BEGIN_DECLS
 #define HUGE_VAL __builtin_huge_val()
 
 /* C99 macros */
-#if __ISO_C_VISIBLE >= 1999 || 1 /* TODO: HACK: Visibility */
+#if __USE_SORTIX || 1999 <= __USE_C
 
 #define FP_ILOGB0 (-__INT_MAX)
 #define FP_ILOGBNAN __INT_MAX
@@ -106,10 +106,10 @@ __BEGIN_DECLS
 typedef __double_t double_t;
 typedef __float_t float_t;
 
-#endif /* __ISO_C_VISIBLE >= 1999 */
+#endif /* __USE_SORTIX || 1999 <= __USE_C */
 
 /* XOPEN/SVID macros */
-#if __BSD_VISIBLE || __XSI_VISIBLE || 1 /* TODO: HACK: Support visibility! */
+#if __USE_SORTIX || __USE_XOPEN
 #define M_E             2.7182818284590452354   /* e */
 #define M_LOG2E         1.4426950408889634074   /* log 2e */
 #define M_LOG10E        0.43429448190325182765  /* log 10e */
@@ -128,11 +128,11 @@ typedef __float_t float_t;
 #define MAXFLOAT        ((float)3.40282346638528860e+38)
 
 extern int signgam;
-#endif /* __BSD_VISIBLE || __XSI_VISIBLE */
+#endif /* __USE_SORTIX || __USE_XOPEN */
 
 /* Various extensions inherited from NetBSD libm. Perhaps we should get rid of
    some of them or make them private to libm itself, or just rename them. */
-#if defined(_NETBSD_SOURCE) || defined(_SORTIX_SOURCE) || 1 /* TODO: HACK: Visibility */
+#if __USE_SORTIX
 enum fdversion {fdlibm_ieee = -1, fdlibm_svid, fdlibm_xopen, fdlibm_posix};
 
 #define _LIB_VERSION_TYPE enum fdversion
@@ -179,7 +179,7 @@ struct exception
 #define TLOSS           5
 #define PLOSS           6
 
-#endif /* _NETBSD_SOURCE */
+#endif /* __USE_SORTIX */
 
 /*
  * Most of these functions depend on the rounding mode and have the side
@@ -219,7 +219,7 @@ double fabs(double);
 double floor(double);
 double fmod(double, double);
 
-#if defined(_XOPEN_SOURCE) || defined(_NETBSD_SOURCE) || 1 /* TODO: HACK: Visibility */
+#if __USE_SORTIX || __USE_XOPEN
 double erf(double);
 double erfc(double);
 double gamma(double);
@@ -232,8 +232,9 @@ double lgamma(double);
 double y0(double);
 double y1(double);
 double yn(int, double);
+#endif  /* __USE_SORTIX || __USE_XOPEN */
 
-#if (_XOPEN_SOURCE - 0) >= 500 || defined(_NETBSD_SOURCE) || 1 /* TODO: HACK: Visibility */
+#if __USE_SORTIX || 500 <= __USE_XOPEN
 double acosh(double);
 double asinh(double);
 double atanh(double);
@@ -246,18 +247,12 @@ double nextafter(double, double);
 double remainder(double, double);
 double rint(double);
 double scalb(double, double);
-#endif /* (_XOPEN_SOURCE - 0) >= 500 || defined(_NETBSD_SOURCE)*/
-#endif /* _XOPEN_SOURCE || _NETBSD_SOURCE */
+#endif /* __USE_SORTIX || 500 <= __USE_XOPEN */
 
 /*
  * ISO C99
  */
-#if !defined(_ANSI_SOURCE) && !defined(_POSIX_C_SOURCE) && \
-    !defined(_XOPEN_SOURCE) || \
-    ((__STDC_VERSION__ - 0) >= 199901L) || \
-    ((_POSIX_C_SOURCE - 0) >= 200112L) || \
-    ((_XOPEN_SOURCE  - 0) >= 600) || \
-    defined(_ISOC99_SOURCE) || defined(_NETBSD_SOURCE) || 1 /* TODO: HACK: Visibility */
+#if __USE_SORTIX || 1999 <= __USE_C
 /* 7.12.3.1 int fpclassify(real-floating x) */
 #define fpclassify(__x) __fpmacro_unary_floating(fpclassify, __x)
 
@@ -379,21 +374,15 @@ long double fdiml(long double, long double);
 long double fmaxl(long double, long double);
 long double fminl(long double, long double);
 
-#endif /* !_ANSI_SOURCE && ... */
-
-#if !defined(_ANSI_SOURCE) && !defined(_POSIX_C_SOURCE) || \
-    !defined(_XOPEN_SOURCE) || \
-    ((__STDC_VERSION__ - 0) >= 199901L) || \
-    ((_POSIX_C_SOURCE - 0) >= 200112L) || \
-    defined(_ISOC99_SOURCE) || defined(_NETBSD_SOURCE) || 1 /* TODO: HACK: Visibility */
 /* 7.12.3.3 int isinf(real-floating x) */
 #define isinf(__x)      __fpmacro_unary_floating(isinf, __x)
 
 /* 7.12.3.4 int isnan(real-floating x) */
 #define isnan(__x)      __fpmacro_unary_floating(isnan, __x)
-#endif /* !_ANSI_SOURCE && ... */
 
-#if defined(_NETBSD_SOURCE) || 1 /* TODO: HACK: Visibility */
+#endif /* __USE_SORTIX || 1999 <= __USE_C */
+
+#if __USE_SORTIX
 #ifndef __cplusplus
 int matherr(struct exception*);
 #endif
@@ -414,19 +403,19 @@ double scalbn(double, int);
  */
 double drem(double, double);
 
-#endif /* _NETBSD_SOURCE */
+#endif /* __USE_SORTIX */
 
-#if defined(_NETBSD_SOURCE) || defined(_REENTRANT) || 1 /* TODO: HACK: Visibility */
+#if __USE_SORTIX /* or _REENTRANT */
 /*
  * Reentrant version of gamma & lgamma; passes signgam back by reference
  * as the second argument; user must allocate space for signgam.
  */
 double gamma_r(double, int*);
 double lgamma_r(double, int*);
-#endif /* _NETBSD_SOURCE || _REENTRANT */
+#endif /* __USE_SORTIX */
 
 
-#if defined(_NETBSD_SOURCE) || 1 /* TODO: HACK: Visibility */
+#if __USE_SORTIX
 
 /* float versions of ANSI/POSIX functions */
 
@@ -452,9 +441,9 @@ float significandf(float);
  * float versions of BSD math library entry points
  */
 float dremf(float, float);
-#endif /* _NETBSD_SOURCE */
+#endif /* __USE_SORTIX */
 
-#if defined(_NETBSD_SOURCE) || defined(_REENTRANT) || 1 /* TODO: HACK: Visibility */
+#if __USE_SORTIX /* or _REENTRANT */
 /*
  * Float versions of reentrant version of gamma & lgamma; passes
  * signgam back by reference as the second argument; user must
@@ -462,7 +451,7 @@ float dremf(float, float);
  */
 float gammaf_r(float, int*);
 float lgammaf_r(float, int*);
-#endif /* !... || _REENTRANT */
+#endif /* __USE_SORTIX */
 
 /*
  * Library implementation
diff --git a/utils/column.cpp b/utils/column.cpp
index a831905b..9a9715a6 100644
--- a/utils/column.cpp
+++ b/utils/column.cpp
@@ -20,8 +20,6 @@
 
 *******************************************************************************/
 
-#define _SORTIX_SOURCE
-
 #include <sys/ioctl.h>
 
 #include <ctype.h>