clarify what isIntegral, isScalar, etc. __traits mean (#3588)

Author: WalterBright

spec/traits.dd

@@ -103,6 +103,8 @@ $(H3 $(GNAME isArithmetic))
         Otherwise, $(D false) is returned.
         If there are no arguments, $(D false) is returned.)
 
+        $(P Arithmetic types are integral types and floating point types.)
+
 $(SPEC_RUNNABLE_EXAMPLE_COMPILE
 ---
 import std.stdio;
@@ -129,8 +131,17 @@ false
 
 $(H3 $(GNAME isFloating))
 
-        $(P Works like $(D isArithmetic), except it's for floating
-        point types (including imaginary and complex types).)
+        $(P If the arguments are all either types that are floating point types,
+        or expressions that are typed as floating point types, then $(D true)
+        is returned.
+        Otherwise, $(D false) is returned.
+        If there are no arguments, $(D false) is returned.)
+
+        $(P The floating point types are:
+        `float`, `double`, `real`,
+        `ifloat`, `idouble`, `ireal`,
+        `cfloat`, `cdouble`, `creal`,
+        vectors of floating point types, and enums with a floating point base type.)
 
 $(SPEC_RUNNABLE_EXAMPLE_COMPILE
 ---
@@ -148,8 +159,16 @@ static assert(!__traits(isFloating, float[4]));
 
 $(H3 $(GNAME isIntegral))
 
-        $(P Works like $(D isArithmetic), except it's for integral
-        types (including character types).)
+        $(P If the arguments are all either types that are integral types,
+        or expressions that are typed as integral types, then $(D true)
+        is returned.
+        Otherwise, $(D false) is returned.
+        If there are no arguments, $(D false) is returned.)
+
+        $(P The integral types are:
+        `byte`, `ubyte`, `short`, `ushort`, `int`, `uint`, `long`, `ulong`, `cent`, `ucent`,
+        `bool`, `char`, `wchar`, `dchar`,
+        vectors of integral types, and enums with an integral base type.)
 
 $(SPEC_RUNNABLE_EXAMPLE_COMPILE
 ---
@@ -171,8 +190,17 @@ static assert(!__traits(isIntegral, void*));
 
 $(H3 $(GNAME isScalar))
 
-        $(P Works like $(D isArithmetic), except it's for scalar
-        types.)
+        $(P If the arguments are all either types that are scalar types,
+        or expressions that are typed as scalar types, then $(D true)
+        is returned.
+        Otherwise, $(D false) is returned.
+        If there are no arguments, $(D false) is returned.)
+
+        $(P Scalar types are integral types,
+        floating point types,
+        pointer types,
+        vectors of scalar types,
+        and enums with a scalar base type.)
 
 $(SPEC_RUNNABLE_EXAMPLE_COMPILE
 ---
@@ -198,8 +226,16 @@ static assert(!__traits(isScalar, Object));
 
 $(H3 $(GNAME isUnsigned))
 
-        $(P Works like $(D isArithmetic), except it's for unsigned
-        types.)
+        $(P If the arguments are all either types that are unsigned types,
+        or expressions that are typed as unsigned types, then $(D true)
+        is returned.
+        Otherwise, $(D false) is returned.
+        If there are no arguments, $(D false) is returned.)
+
+        $(P The unsigned types are:
+        `ubyte`, `ushort`, `uint`, `ulong`, `ucent`,
+        `bool`, `char`, `wchar`, `dchar`,
+        vectors of unsigned types, and enums with an unsigned base type.)
 
 $(SPEC_RUNNABLE_EXAMPLE_COMPILE
 ---