diff --git a/include/SDL3/SDL_bits.h b/include/SDL3/SDL_bits.h
index d4a3aff35..1c76d1570 100644
--- a/include/SDL3/SDL_bits.h
+++ b/include/SDL3/SDL_bits.h
@@ -40,13 +40,6 @@ extern "C" {
  *  \file SDL_bits.h
  */
 
-/**
- *  Get the index of the most significant bit. Result is undefined when called
- *  with 0. This operation can also be stated as "count leading zeroes" and
- *  "log base 2".
- *
- *  \return the index of the most significant bit, or -1 if the value is 0.
- */
 #if defined(__WATCOMC__) && defined(__386__)
 extern __inline int _SDL_bsr_watcom(Uint32);
 #pragma aux _SDL_bsr_watcom = \
@@ -56,8 +49,25 @@ extern __inline int _SDL_bsr_watcom(Uint32);
     modify exact [eax] nomemory;
 #endif
 
-SDL_FORCE_INLINE int
-SDL_MostSignificantBitIndex32(Uint32 x)
+/**
+ * Get the index of the most significant (set) bit in a 32-bit number.
+ *
+ * Result is undefined when called with 0. This operation can also be
+ * stated as "count leading zeroes" and "log base 2".
+ *
+ * Note that this is a forced-inline function in a header, and not a public
+ * API function available in the SDL library (which is to say, the code is
+ * embedded in the calling program and the linker and dynamic loader will
+ * not be able to find this function inside SDL itself).
+ *
+ * \param x the 32-bit value to examine
+ * \returns the index of the most significant bit, or -1 if the value is 0.
+ *
+ * \threadsafety It is safe to call this function from any thread.
+ *
+ * \since This function is available since SDL 3.0.0.
+ */
+SDL_FORCE_INLINE int SDL_MostSignificantBitIndex32(Uint32 x)
 {
 #if defined(__GNUC__) && (__GNUC__ >= 4 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4))
     /* Count Leading Zeroes builtin in GCC.
@@ -106,8 +116,26 @@ SDL_MostSignificantBitIndex32(Uint32 x)
 #endif
 }
 
-SDL_FORCE_INLINE SDL_bool
-SDL_HasExactlyOneBitSet32(Uint32 x)
+/**
+ * Determine if a unsigned 32-bit value has exactly one bit set.
+ *
+ * If there are no bits set (`x` is zero), or more than one bit set, this
+ * returns SDL_FALSE. If any one bit is exclusively set, this returns
+ * SDL_TRUE.
+ *
+ * Note that this is a forced-inline function in a header, and not a public
+ * API function available in the SDL library (which is to say, the code is
+ * embedded in the calling program and the linker and dynamic loader will
+ * not be able to find this function inside SDL itself).
+ *
+ * \param x the 32-bit value to examine
+ * \returns SDL_TRUE if exactly one bit is set in `x`, SDL_FALSE otherwise.
+ *
+ * \threadsafety It is safe to call this function from any thread.
+ *
+ * \since This function is available since SDL 3.0.0.
+ */
+SDL_FORCE_INLINE SDL_bool SDL_HasExactlyOneBitSet32(Uint32 x)
 {
     if (x && !(x & (x - 1))) {
         return SDL_TRUE;
diff --git a/include/SDL3/SDL_endian.h b/include/SDL3/SDL_endian.h
index fb2c62054..7021132bd 100644
--- a/include/SDL3/SDL_endian.h
+++ b/include/SDL3/SDL_endian.h
@@ -138,31 +138,26 @@ extern "C" {
 #   define HAS_BROKEN_BSWAP 0
 #endif
 
-/**
- * Byte swap 16-bit integer.
- */
+/* Byte swap 16-bit integer. */
 #if HAS_BUILTIN_BSWAP16
 #define SDL_Swap16(x) __builtin_bswap16(x)
 #elif (defined(_MSC_VER) && (_MSC_VER >= 1400)) && !defined(__ICL)
 #pragma intrinsic(_byteswap_ushort)
 #define SDL_Swap16(x) _byteswap_ushort(x)
 #elif defined(__i386__) && !HAS_BROKEN_BSWAP
-SDL_FORCE_INLINE Uint16
-SDL_Swap16(Uint16 x)
+SDL_FORCE_INLINE Uint16 SDL_Swap16(Uint16 x)
 {
   __asm__("xchgb %b0,%h0": "=q"(x):"0"(x));
     return x;
 }
 #elif defined(__x86_64__)
-SDL_FORCE_INLINE Uint16
-SDL_Swap16(Uint16 x)
+SDL_FORCE_INLINE Uint16 SDL_Swap16(Uint16 x)
 {
   __asm__("xchgb %b0,%h0": "=Q"(x):"0"(x));
     return x;
 }
 #elif (defined(__powerpc__) || defined(__ppc__))
-SDL_FORCE_INLINE Uint16
-SDL_Swap16(Uint16 x)
+SDL_FORCE_INLINE Uint16 SDL_Swap16(Uint16 x)
 {
     int result;
 
@@ -170,8 +165,7 @@ SDL_Swap16(Uint16 x)
     return (Uint16)result;
 }
 #elif (defined(__m68k__) && !defined(__mcoldfire__))
-SDL_FORCE_INLINE Uint16
-SDL_Swap16(Uint16 x)
+SDL_FORCE_INLINE Uint16 SDL_Swap16(Uint16 x)
 {
   __asm__("rorw #8,%0": "=d"(x): "0"(x):"cc");
     return x;
@@ -183,38 +177,32 @@ extern __inline Uint16 SDL_Swap16(Uint16);
   parm   [ax]   \
   modify [ax];
 #else
-SDL_FORCE_INLINE Uint16
-SDL_Swap16(Uint16 x)
+SDL_FORCE_INLINE Uint16 SDL_Swap16(Uint16 x)
 {
     return SDL_static_cast(Uint16, ((x << 8) | (x >> 8)));
 }
 #endif
 
-/**
- * Byte swap 32-bit integer.
- */
+/* Byte swap 32-bit integer. */
 #if HAS_BUILTIN_BSWAP32
 #define SDL_Swap32(x) __builtin_bswap32(x)
 #elif (defined(_MSC_VER) && (_MSC_VER >= 1400)) && !defined(__ICL)
 #pragma intrinsic(_byteswap_ulong)
 #define SDL_Swap32(x) _byteswap_ulong(x)
 #elif defined(__i386__) && !HAS_BROKEN_BSWAP
-SDL_FORCE_INLINE Uint32
-SDL_Swap32(Uint32 x)
+SDL_FORCE_INLINE Uint32 SDL_Swap32(Uint32 x)
 {
   __asm__("bswap %0": "=r"(x):"0"(x));
     return x;
 }
 #elif defined(__x86_64__)
-SDL_FORCE_INLINE Uint32
-SDL_Swap32(Uint32 x)
+SDL_FORCE_INLINE Uint32 SDL_Swap32(Uint32 x)
 {
   __asm__("bswapl %0": "=r"(x):"0"(x));
     return x;
 }
 #elif (defined(__powerpc__) || defined(__ppc__))
-SDL_FORCE_INLINE Uint32
-SDL_Swap32(Uint32 x)
+SDL_FORCE_INLINE Uint32 SDL_Swap32(Uint32 x)
 {
     Uint32 result;
 
@@ -224,8 +212,7 @@ SDL_Swap32(Uint32 x)
     return result;
 }
 #elif (defined(__m68k__) && !defined(__mcoldfire__))
-SDL_FORCE_INLINE Uint32
-SDL_Swap32(Uint32 x)
+SDL_FORCE_INLINE Uint32 SDL_Swap32(Uint32 x)
 {
   __asm__("rorw #8,%0\n\tswap %0\n\trorw #8,%0": "=d"(x): "0"(x):"cc");
     return x;
@@ -237,17 +224,14 @@ extern __inline Uint32 SDL_Swap32(Uint32);
   parm   [eax] \
   modify [eax];
 #else
-SDL_FORCE_INLINE Uint32
-SDL_Swap32(Uint32 x)
+SDL_FORCE_INLINE Uint32 SDL_Swap32(Uint32 x)
 {
     return SDL_static_cast(Uint32, ((x << 24) | ((x << 8) & 0x00FF0000) |
                                     ((x >> 8) & 0x0000FF00) | (x >> 24)));
 }
 #endif
 
-/**
- * Byte swap 64-bit integer.
- */
+/* Byte swap 64-bit integer. */
 #if HAS_BUILTIN_BSWAP64
 #define SDL_Swap64(x) __builtin_bswap64(x)
 #elif (defined(_MSC_VER) && (_MSC_VER >= 1400)) && !defined(__ICL)
@@ -270,8 +254,7 @@ SDL_Swap64(Uint64 x)
     return v.u;
 }
 #elif defined(__x86_64__)
-SDL_FORCE_INLINE Uint64
-SDL_Swap64(Uint64 x)
+SDL_FORCE_INLINE Uint64 SDL_Swap64(Uint64 x)
 {
   __asm__("bswapq %0": "=r"(x):"0"(x));
     return x;
@@ -285,8 +268,7 @@ extern __inline Uint64 SDL_Swap64(Uint64);
   parm [eax edx]  \
   modify [eax edx];
 #else
-SDL_FORCE_INLINE Uint64
-SDL_Swap64(Uint64 x)
+SDL_FORCE_INLINE Uint64 SDL_Swap64(Uint64 x)
 {
     Uint32 hi, lo;
 
@@ -303,10 +285,25 @@ SDL_Swap64(Uint64 x)
 
 
 /**
- * Byte swap floating point number.
+ * Byte-swap a floating point number.
+ *
+ * This will always byte-swap the value, whether it's currently in the native
+ * byteorder of the system or not. You should use SDL_SwapFloatLE or
+ * SDL_SwapFloatBE instead, in most cases.
+ *
+ * Note that this is a forced-inline function in a header, and not a public
+ * API function available in the SDL library (which is to say, the code is
+ * embedded in the calling program and the linker and dynamic loader will
+ * not be able to find this function inside SDL itself).
+ *
+ * \param x the value to byte-swap.
+ * \returns x, with its bytes in the opposite endian order.
+ *
+ * \threadsafety It is safe to call this function from any thread.
+ *
+ * \since This function is available since SDL 3.0.0.
  */
-SDL_FORCE_INLINE float
-SDL_SwapFloat(float x)
+SDL_FORCE_INLINE float SDL_SwapFloat(float x)
 {
     union {
         float f;
@@ -325,137 +322,199 @@ SDL_SwapFloat(float x)
 
 
 #ifdef SDL_WIKI_DOCUMENTATION_SECTION
+/**
+ * Byte-swap an unsigned 16-bit number.
+ *
+ * This will always byte-swap the value, whether it's currently in the native
+ * byteorder of the system or not. You should use SDL_SwapLE16 or
+ * SDL_SwapBE16 instead, in most cases.
+ *
+ * Note that this is a forced-inline function in a header, and not a public
+ * API function available in the SDL library (which is to say, the code is
+ * embedded in the calling program and the linker and dynamic loader will
+ * not be able to find this function inside SDL itself).
+ *
+ * \param x the value to byte-swap.
+ * \returns `x`, with its bytes in the opposite endian order.
+ *
+ * \threadsafety It is safe to call this function from any thread.
+ *
+ * \since This function is available since SDL 3.0.0.
+ */
+SDL_FORCE_INLINE Uint16 SDL_Swap16(Uint16 x) { return x_but_byteswapped; }
 
 /**
- * Swap a 16-bit value from littleendian to native format.
+ * Byte-swap an unsigned 32-bit number.
  *
- * If this is running on a littleendian system, `X` is returned unchanged.
+ * This will always byte-swap the value, whether it's currently in the native
+ * byteorder of the system or not. You should use SDL_SwapLE32 or
+ * SDL_SwapBE32 instead, in most cases.
  *
- * This macro never references `X` more than once, avoiding side effects.
+ * Note that this is a forced-inline function in a header, and not a public
+ * API function available in the SDL library (which is to say, the code is
+ * embedded in the calling program and the linker and dynamic loader will
+ * not be able to find this function inside SDL itself).
  *
- * \param X the value to swap.
- * \returns the byte-swapped value.
+ * \param x the value to byte-swap.
+ * \returns `x`, with its bytes in the opposite endian order.
+ *
+ * \threadsafety It is safe to call this function from any thread.
+ *
+ * \since This function is available since SDL 3.0.0.
+ */
+SDL_FORCE_INLINE Uint32 SDL_Swap32(Uint32 x) { return x_but_byteswapped; }
+
+/**
+ * Byte-swap an unsigned 64-bit number.
+ *
+ * This will always byte-swap the value, whether it's currently in the native
+ * byteorder of the system or not. You should use SDL_SwapLE64 or
+ * SDL_SwapBE64 instead, in most cases.
+ *
+ * Note that this is a forced-inline function in a header, and not a public
+ * API function available in the SDL library (which is to say, the code is
+ * embedded in the calling program and the linker and dynamic loader will
+ * not be able to find this function inside SDL itself).
+ *
+ * \param x the value to byte-swap.
+ * \returns `x`, with its bytes in the opposite endian order.
+ *
+ * \threadsafety It is safe to call this function from any thread.
+ *
+ * \since This function is available since SDL 3.0.0.
+ */
+SDL_FORCE_INLINE Uint32 SDL_Swap64(Uint64 x) { return x_but_byteswapped; }
+
+/**
+ * Swap a 16-bit value from littleendian to native byte order.
+ *
+ * If this is running on a littleendian system, `x` is returned unchanged.
+ *
+ * This macro never references `x` more than once, avoiding side effects.
+ *
+ * \param x the value to swap, in littleendian byte order.
+ * \returns `x` in native byte order.
  *
  * \since This macro is available since SDL 3.0.0.
  */
-#define SDL_SwapLE16(X) SwapOnlyIfNecessary(X)
+#define SDL_SwapLE16(x) SwapOnlyIfNecessary(x)
 
 /**
- * Swap a 32-bit value from littleendian to native format.
+ * Swap a 32-bit value from littleendian to native byte order.
  *
- * If this is running on a littleendian system, `X` is returned unchanged.
+ * If this is running on a littleendian system, `x` is returned unchanged.
  *
- * This macro never references `X` more than once, avoiding side effects.
+ * This macro never references `x` more than once, avoiding side effects.
  *
- * \param X the value to swap.
- * \returns the byte-swapped value.
+ * \param x the value to swap, in littleendian byte order.
+ * \returns `x` in native byte order.
  *
  * \since This macro is available since SDL 3.0.0.
  */
-#define SDL_SwapLE32(X) SwapOnlyIfNecessary(X)
+#define SDL_SwapLE32(x) SwapOnlyIfNecessary(x)
 
 /**
- * Swap a 64-bit value from littleendian to native format.
+ * Swap a 64-bit value from littleendian to native byte order.
  *
- * If this is running on a littleendian system, `X` is returned unchanged.
+ * If this is running on a littleendian system, `x` is returned unchanged.
  *
- * This macro never references `X` more than once, avoiding side effects.
+ * This macro never references `x` more than once, avoiding side effects.
  *
- * \param X the value to swap.
- * \returns the byte-swapped value.
+ * \param x the value to swap, in littleendian byte order.
+ * \returns `x` in native byte order.
  *
  * \since This macro is available since SDL 3.0.0.
  */
-#define SDL_SwapLE64(X) SwapOnlyIfNecessary(X)
+#define SDL_SwapLE64(x) SwapOnlyIfNecessary(x)
 
 /**
- * Swap a floating point value from littleendian to native format.
+ * Swap a floating point value from littleendian to native byte order.
  *
- * If this is running on a littleendian system, `X` is returned unchanged.
+ * If this is running on a littleendian system, `x` is returned unchanged.
  *
- * This macro never references `X` more than once, avoiding side effects.
+ * This macro never references `x` more than once, avoiding side effects.
  *
- * \param X the value to swap.
- * \returns the byte-swapped value.
+ * \param x the value to swap, in littleendian byte order.
+ * \returns `x` in native byte order.
  *
  * \since This macro is available since SDL 3.0.0.
  */
-#define SDL_SwapFloatLE(X) SwapOnlyIfNecessary(X)
+#define SDL_SwapFloatLE(x) SwapOnlyIfNecessary(x)
 
 /**
- * Swap a 16-bit value from bigendian to native format.
+ * Swap a 16-bit value from bigendian to native byte order.
  *
- * If this is running on a bigendian system, `X` is returned unchanged.
+ * If this is running on a bigendian system, `x` is returned unchanged.
  *
- * This macro never references `X` more than once, avoiding side effects.
+ * This macro never references `x` more than once, avoiding side effects.
  *
- * \param X the value to swap.
- * \returns the byte-swapped value.
+ * \param x the value to swap, in bigendian byte order.
+ * \returns `x` in native byte order.
  *
  * \since This macro is available since SDL 3.0.0.
  */
-#define SDL_SwapBE16(X) SwapOnlyIfNecessary(X)
+#define SDL_SwapBE16(x) SwapOnlyIfNecessary(x)
 
 /**
- * Swap a 32-bit value from bigendian to native format.
+ * Swap a 32-bit value from bigendian to native byte order.
  *
- * If this is running on a bigendian system, `X` is returned unchanged.
+ * If this is running on a bigendian system, `x` is returned unchanged.
  *
- * This macro never references `X` more than once, avoiding side effects.
+ * This macro never references `x` more than once, avoiding side effects.
  *
- * \param X the value to swap.
- * \returns the byte-swapped value.
+ * \param x the value to swap, in bigendian byte order.
+ * \returns `x` in native byte order.
  *
  * \since This macro is available since SDL 3.0.0.
  */
-#define SDL_SwapBE32(X) SwapOnlyIfNecessary(X)
+#define SDL_SwapBE32(x) SwapOnlyIfNecessary(x)
 
 /**
- * Swap a 64-bit value from bigendian to native format.
+ * Swap a 64-bit value from bigendian to native byte order.
  *
- * If this is running on a bigendian system, `X` is returned unchanged.
+ * If this is running on a bigendian system, `x` is returned unchanged.
  *
- * This macro never references `X` more than once, avoiding side effects.
+ * This macro never references `x` more than once, avoiding side effects.
  *
- * \param X the value to swap.
- * \returns the byte-swapped value.
+ * \param x the value to swap, in bigendian byte order.
+ * \returns `x` in native byte order.
  *
  * \since This macro is available since SDL 3.0.0.
  */
-#define SDL_SwapBE64(X) SwapOnlyIfNecessary(X)
+#define SDL_SwapBE64(x) SwapOnlyIfNecessary(x)
 
 /**
- * Swap a floating point value from bigendian to native format.
+ * Swap a floating point value from bigendian to native byte order.
  *
- * If this is running on a bigendian system, `X` is returned unchanged.
+ * If this is running on a bigendian system, `x` is returned unchanged.
  *
- * This macro never references `X` more than once, avoiding side effects.
+ * This macro never references `x` more than once, avoiding side effects.
  *
- * \param X the value to swap.
- * \returns the byte-swapped value.
+ * \param x the value to swap, in bigendian byte order.
+ * \returns `x` in native byte order.
  *
  * \since This macro is available since SDL 3.0.0.
  */
-#define SDL_SwapFloatBE(X) SwapOnlyIfNecessary(X)
+#define SDL_SwapFloatBE(x) SwapOnlyIfNecessary(x)
 
 #elif SDL_BYTEORDER == SDL_LIL_ENDIAN
-#define SDL_SwapLE16(X)     (X)
-#define SDL_SwapLE32(X)     (X)
-#define SDL_SwapLE64(X)     (X)
-#define SDL_SwapFloatLE(X)  (X)
-#define SDL_SwapBE16(X)     SDL_Swap16(X)
-#define SDL_SwapBE32(X)     SDL_Swap32(X)
-#define SDL_SwapBE64(X)     SDL_Swap64(X)
-#define SDL_SwapFloatBE(X)  SDL_SwapFloat(X)
+#define SDL_SwapLE16(x)     (x)
+#define SDL_SwapLE32(x)     (x)
+#define SDL_SwapLE64(x)     (x)
+#define SDL_SwapFloatLE(x)  (x)
+#define SDL_SwapBE16(x)     SDL_Swap16(x)
+#define SDL_SwapBE32(x)     SDL_Swap32(x)
+#define SDL_SwapBE64(x)     SDL_Swap64(x)
+#define SDL_SwapFloatBE(x)  SDL_SwapFloat(x)
 #else
-#define SDL_SwapLE16(X)     SDL_Swap16(X)
-#define SDL_SwapLE32(X)     SDL_Swap32(X)
-#define SDL_SwapLE64(X)     SDL_Swap64(X)
-#define SDL_SwapFloatLE(X)  SDL_SwapFloat(X)
-#define SDL_SwapBE16(X)     (X)
-#define SDL_SwapBE32(X)     (X)
-#define SDL_SwapBE64(X)     (X)
-#define SDL_SwapFloatBE(X)  (X)
+#define SDL_SwapLE16(x)     SDL_Swap16(x)
+#define SDL_SwapLE32(x)     SDL_Swap32(x)
+#define SDL_SwapLE64(x)     SDL_Swap64(x)
+#define SDL_SwapFloatLE(x)  SDL_SwapFloat(x)
+#define SDL_SwapBE16(x)     (x)
+#define SDL_SwapBE32(x)     (x)
+#define SDL_SwapBE64(x)     (x)
+#define SDL_SwapFloatBE(x)  (x)
 #endif
 
 /* Ends C function definitions when using C++ */
diff --git a/include/SDL3/SDL_rect.h b/include/SDL3/SDL_rect.h
index fd9aabfa0..616a02642 100644
--- a/include/SDL3/SDL_rect.h
+++ b/include/SDL3/SDL_rect.h
@@ -112,16 +112,49 @@ typedef struct SDL_FRect
 
 
 /**
- * Returns true if point resides inside a rectangle.
+ * Determine whether a point resides inside a rectangle.
+ *
+ * A point is considered part of a rectangle if both `p` and `r` are
+ * not NULL, and `p`'s x and y coordinates are >= to the rectangle's
+ * top left corner, and < the rectangle's x+w and y+h. So a 1x1 rectangle
+ * considers point (0,0) as "inside" and (0,1) as not.
+ *
+ * Note that this is a forced-inline function in a header, and not a public
+ * API function available in the SDL library (which is to say, the code is
+ * embedded in the calling program and the linker and dynamic loader will
+ * not be able to find this function inside SDL itself).
+ *
+ * \param p the point to test.
+ * \param r the rectangle to test.
+ * \returns SDL_TRUE if `p` is contained by `r`, SDL_FALSE otherwise.
+ *
+ * \threadsafety It is safe to call this function from any thread.
+ *
+ * \since This function is available since SDL 3.0.0.
  */
 SDL_FORCE_INLINE SDL_bool SDL_PointInRect(const SDL_Point *p, const SDL_Rect *r)
 {
-    return ( (p->x >= r->x) && (p->x < (r->x + r->w)) &&
+    return ( p && r && (p->x >= r->x) && (p->x < (r->x + r->w)) &&
              (p->y >= r->y) && (p->y < (r->y + r->h)) ) ? SDL_TRUE : SDL_FALSE;
 }
 
 /**
- * Returns true if the rectangle has no area.
+ * Determine whether a rectangle has no area.
+ *
+ * A rectangle is considered "empty" for this function if `r` is NULL,
+ * or if `r`'s width and/or height are <= 0.
+ *
+ * Note that this is a forced-inline function in a header, and not a public
+ * API function available in the SDL library (which is to say, the code is
+ * embedded in the calling program and the linker and dynamic loader will
+ * not be able to find this function inside SDL itself).
+ *
+ * \param r the rectangle to test.
+ * \returns SDL_TRUE if the rectangle is "empty", SDL_FALSE otherwise.
+ *
+ * \threadsafety It is safe to call this function from any thread.
+ *
+ * \since This function is available since SDL 3.0.0.
  */
 SDL_FORCE_INLINE SDL_bool SDL_RectEmpty(const SDL_Rect *r)
 {
@@ -129,7 +162,23 @@ SDL_FORCE_INLINE SDL_bool SDL_RectEmpty(const SDL_Rect *r)
 }
 
 /**
- * Returns true if the two rectangles are equal.
+ * Determine whether two rectangles are equal.
+ *
+ * Rectangles are considered equal if both are not NULL and each of their
+ * x, y, width and height match.
+ *
+ * Note that this is a forced-inline function in a header, and not a public
+ * API function available in the SDL library (which is to say, the code is
+ * embedded in the calling program and the linker and dynamic loader will
+ * not be able to find this function inside SDL itself).
+ *
+ * \param a the first rectangle to test.
+ * \param b the second rectangle to test.
+ * \returns SDL_TRUE if the rectangles are equal, SDL_FALSE otherwise.
+ *
+ * \threadsafety It is safe to call this function from any thread.
+ *
+ * \since This function is available since SDL 3.0.0.
  */
 SDL_FORCE_INLINE SDL_bool SDL_RectsEqual(const SDL_Rect *a, const SDL_Rect *b)
 {
@@ -146,12 +195,14 @@ SDL_FORCE_INLINE SDL_bool SDL_RectsEqual(const SDL_Rect *a, const SDL_Rect *b)
  * \param B an SDL_Rect structure representing the second rectangle
  * \returns SDL_TRUE if there is an intersection, SDL_FALSE otherwise.
  *
+ * \threadsafety It is safe to call this function from any thread.
+ *
  * \since This function is available since SDL 3.0.0.
  *
  * \sa SDL_GetRectIntersection
  */
 extern DECLSPEC SDL_bool SDLCALL SDL_HasRectIntersection(const SDL_Rect * A,
-                                                     const SDL_Rect * B);
+                                                         const SDL_Rect * B);
 
 /**
  * Calculate the intersection of two rectangles.
@@ -237,16 +288,47 @@ extern DECLSPEC SDL_bool SDLCALL SDL_GetRectAndLineIntersection(const SDL_Rect *
 /* SDL_FRect versions... */
 
 /**
- * Returns true if point resides inside a rectangle.
+ * Determine whether a point resides inside a floating point rectangle.
+ *
+ * A point is considered part of a rectangle if both `p` and `r` are
+ * not NULL, and `p`'s x and y coordinates are >= to the rectangle's
+ * top left corner, and < the rectangle's x+w and y+h. So a 1x1 rectangle
+ * considers point (0,0) as "inside" and (0,1) as not.
+ *
+ * Note that this is a forced-inline function in a header, and not a public
+ * API function available in the SDL library (which is to say, the code is
+ * embedded in the calling program and the linker and dynamic loader will
+ * not be able to find this function inside SDL itself).
+ *
+ * \param p the point to test.
+ * \param r the rectangle to test.
+ * \returns SDL_TRUE if `p` is contained by `r`, SDL_FALSE otherwise.
+ *
+ * \threadsafety It is safe to call this function from any thread.
+ *
+ * \since This function is available since SDL 3.0.0.
  */
 SDL_FORCE_INLINE SDL_bool SDL_PointInRectFloat(const SDL_FPoint *p, const SDL_FRect *r)
 {
-    return ( (p->x >= r->x) && (p->x < (r->x + r->w)) &&
+    return ( p && r && (p->x >= r->x) && (p->x < (r->x + r->w)) &&
              (p->y >= r->y) && (p->y < (r->y + r->h)) ) ? SDL_TRUE : SDL_FALSE;
 }
 
 /**
- * Returns true if the rectangle has no area.
+ * Determine whether a floating point rectangle has no area.
+ *
+ * A rectangle is considered "empty" for this function if `r` is NULL,
+ * or if `r`'s width and/or height are <= 0.0f.
+ *
+ * Note that this is a forced-inline function in a header, and not a public
+ * API function available in the SDL library (which is to say, the code is
+ * embedded in the calling program and the linker and dynamic loader will
+ * not be able to find this function inside SDL itself).
+ *
+ * \param r the rectangle to test.
+ * \returns SDL_TRUE if the rectangle is "empty", SDL_FALSE otherwise.
+ *
+ * \threadsafety It is safe to call this function from any thread.
  *
  * \since This function is available since SDL 3.0.0.
  */
@@ -256,9 +338,27 @@ SDL_FORCE_INLINE SDL_bool SDL_RectEmptyFloat(const SDL_FRect *r)
 }
 
 /**
- * Returns true if the two rectangles are equal, within some given epsilon.
+ * Determine whether two floating point rectangles are equal, within some given epsilon.
+ *
+ * Rectangles are considered equal if both are not NULL and each of their
+ * x, y, width and height are within `epsilon` of each other. If you don't
+ * know what value to use for `epsilon`, you should call the
+ * SDL_RectsEqualFloat function instead.
+ *
+ * Note that this is a forced-inline function in a header, and not a public
+ * API function available in the SDL library (which is to say, the code is
+ * embedded in the calling program and the linker and dynamic loader will
+ * not be able to find this function inside SDL itself).
+ *
+ * \param a the first rectangle to test.
+ * \param b the second rectangle to test.
+ * \returns SDL_TRUE if the rectangles are equal, SDL_FALSE otherwise.
+ *
+ * \threadsafety It is safe to call this function from any thread.
  *
  * \since This function is available since SDL 3.0.0.
+ *
+ * \sa SDL_RectsEqualFloat
  */
 SDL_FORCE_INLINE SDL_bool SDL_RectsEqualEpsilon(const SDL_FRect *a, const SDL_FRect *b, const float epsilon)
 {
@@ -271,9 +371,28 @@ SDL_FORCE_INLINE SDL_bool SDL_RectsEqualEpsilon(const SDL_FRect *a, const SDL_FR
 }
 
 /**
- * Returns true if the two rectangles are equal, using a default epsilon.
+ * Determine whether two floating point rectangles are equal, within a default epsilon.
+ *
+ * Rectangles are considered equal if both are not NULL and each of their
+ * x, y, width and height are within SDL_FLT_EPSILON of each other. This is
+ * often a reasonable way to compare two floating point rectangles and
+ * deal with the slight precision variations in floating point calculations
+ * that tend to pop up.
+ *
+ * Note that this is a forced-inline function in a header, and not a public
+ * API function available in the SDL library (which is to say, the code is
+ * embedded in the calling program and the linker and dynamic loader will
+ * not be able to find this function inside SDL itself).
+ *
+ * \param a the first rectangle to test.
+ * \param b the second rectangle to test.
+ * \returns SDL_TRUE if the rectangles are equal, SDL_FALSE otherwise.
+ *
+ * \threadsafety It is safe to call this function from any thread.
  *
  * \since This function is available since SDL 3.0.0.
+ *
+ * \sa SDL_RectsEqualEpsilon
  */
 SDL_FORCE_INLINE SDL_bool SDL_RectsEqualFloat(const SDL_FRect *a, const SDL_FRect *b)
 {