[std] Remove problematic 'requires' phrases from notes.

Only specific phrases involving the word "required" are problematic,
namely when they appear to establish a normative requirement. They
have been reworded, often by replacing "is required" with "needs",
sometimes with slightly larger edits.

source/basic.tex

@@ -6538,7 +6538,7 @@
 the implementation ensures that the thread will eventually make progress for as
 long as it has not terminated.
 \begin{note}
-This is required regardless of whether or not other threads of execution (if any)
+This is regardless of whether or not other threads of execution (if any)
 have been or are making progress. To eventually fulfill this requirement means that
 this will happen in an unspecified but finite amount of time.
 \end{note}

source/classes.tex

@@ -1330,7 +1330,7 @@
 \indextext{constructor!implicitly invoked}%
 A default constructor is implicitly invoked to initialize
 a class object when no initializer is specified\iref{dcl.init.general}.
-Such a default constructor is required to be accessible\iref{class.access}.
+Such a default constructor needs to be accessible\iref{class.access}.
 \end{note}
 
 \pnum

source/containers.tex

@@ -2719,7 +2719,7 @@
 and \tcode{mapped_type}.
 \begin{note}
 For example, in some cases \tcode{key_type} and \tcode{mapped_type}
-are required to be \oldconcept{CopyAssignable} even though the associated
+need to be \oldconcept{CopyAssignable} even though the associated
 \tcode{value_type}, \tcode{pair<const key_type, mapped_type>}, is not
 \oldconcept{CopyAssignable}.
 \end{note}
@@ -4217,7 +4217,7 @@
 apply instead to \tcode{key_type} and \tcode{mapped_type}.
 \begin{note}
 For example, \tcode{key_type} and \tcode{mapped_type}
-are sometimes required to be \oldconcept{CopyAssignable}
+sometimes need to be \oldconcept{CopyAssignable}
 even though the associated \tcode{value_type},
 \tcode{pair<const key_type, mapped_type>},
 is not \oldconcept{CopyAssignable}.

source/declarations.tex

@@ -1268,10 +1268,10 @@
 \indextext{\idxcode{volatile}!implementation-defined}%
 \begin{note}
 \tcode{volatile} is a hint to the implementation to avoid aggressive
-optimization involving the object because the value of the object might
-be changed by means undetectable by an implementation.
-Furthermore, for some implementations, \tcode{volatile} might indicate that
-special hardware instructions are required to access the object.
+optimization involving the object because it is possible for the value of the object
+to change by means undetectable by an implementation.
+Furthermore, for some implementations, \tcode{volatile} can indicate that
+special hardware instructions are needed to access the object.
 See~\ref{intro.execution} for detailed semantics. In general, the
 semantics of \tcode{volatile} are intended to be the same in \Cpp{} as
 they are in C.
@@ -5394,8 +5394,7 @@
 \begin{note}
 As specified above, brace elision cannot apply to
 subaggregates with no elements; an
-\grammarterm{initializer-clause} for the entire subobject is
-required.
+\grammarterm{initializer-clause} for the entire subobject is needed.
 \end{note}
 
 \begin{example}
@@ -6084,7 +6083,7 @@
 corresponding element of the initializer list, and the
 \tcode{std::initializer_list<E>} object is constructed to refer to that array.
 \begin{note}
-A constructor or conversion function selected for the copy is required to be
+A constructor or conversion function selected for the copy needs to be
 accessible\iref{class.access} in the context of the initializer list.
 \end{note}
 If a narrowing conversion is required to initialize any of the elements,

source/expressions.tex

@@ -1412,7 +1412,7 @@
 \end{codeblock}
 In each case, the constraints of \tcode{f} are not satisfied.
 In the declaration of \tcode{p2},
-those constraints are required to be satisfied
+those constraints need to be satisfied
 even though
 \tcode{f} is an unevaluated operand\iref{term.unevaluated.operand}.
 \end{example}
@@ -2182,7 +2182,7 @@
 if the function call operator template specialization is an immediate function.
 \begin{note}
 This will result in the implicit instantiation of the generic lambda's body.
-The instantiated generic lambda's return type and parameter types are required to match
+The instantiated generic lambda's return type and parameter types need to match
 the return type and parameter types of the pointer to function.
 \end{note}
 \begin{example}
@@ -3404,7 +3404,7 @@
 A function can change the values of its non-const parameters, but these
 changes cannot affect the values of the arguments except where a
 parameter is of a reference type\iref{dcl.ref}; if the reference is to
-a const-qualified type, \keyword{const_cast} is required to be used to
+a const-qualified type, \keyword{const_cast} needs to be used to
 cast away the constness in order to modify the argument's value. Where a
 parameter is of \keyword{const} reference type a temporary object is
 introduced if
@@ -5378,7 +5378,7 @@
 and the deallocation function's name is
 \tcode{\keyword{operator} \keyword{delete}[]}.
 \begin{note}
-An implementation is required to provide default definitions for the global
+An implementation is expected to provide default definitions for the global
 allocation
 functions\iref{basic.stc.dynamic,new.delete.single,new.delete.array}.
 A \Cpp{} program can provide alternative definitions of

source/iostreams.tex

@@ -918,7 +918,7 @@
 to class \tcode{ios_base::failure} shown in this subclause.
 \begin{note}
 When \tcode{ios_base::failure} is a synonym for another type,
-that type is required to provide a nested type \tcode{failure}
+that type needs to provide a nested type \tcode{failure}
 to emulate the injected-class-name.
 \end{note}
 The class
@@ -14384,7 +14384,7 @@
 \effects
 Each \grammarterm{directory-separator}
 of the pathname in the generic format
-  is converted to \grammarterm{preferred-separator}.
+is converted to \grammarterm{preferred-separator}.
 
 \pnum
 \returns
@@ -15161,8 +15161,8 @@
 \item The \grammarterm{root-name} element, if present.
 \item The \grammarterm{root-directory} element, if present.
 \begin{note}
-The generic format is required to ensure lexicographical
-comparison works correctly.
+It is possible that the use of the generic format is needed
+to ensure correct lexicographical comparison.
 \end{note}
 \item Each successive \grammarterm{filename} element, if present.
 \item An empty element, if a trailing non-root \grammarterm{directory-separator}

source/lex.tex

@@ -665,8 +665,7 @@
 (collectively, ``whitespace''), as described below, are ignored except
 as they serve to separate tokens.
 \begin{note}
-Some whitespace is
-required to separate otherwise adjacent identifiers, keywords, numeric
+Whitespace can separate otherwise adjacent identifiers, keywords, numeric
 literals, and alternative tokens containing alphabetic characters.
 \end{note}
 \indextext{token|)}
@@ -1851,7 +1850,7 @@
 
 \pnum
 \begin{note}
-The characters \tcode{'('} and \tcode{')'} are permitted in a
+The characters \tcode{'('} and \tcode{')'} can appear in a
 \grammarterm{raw-string}. Thus, \tcode{R"delimiter((a|b))delimiter"} is equivalent to
 \tcode{"(a|b)"}.
 \end{note}

source/lib-intro.tex

@@ -1289,16 +1289,16 @@
 Names which are defined as macros in C shall be defined as macros in the \Cpp{}
 standard library, even if C grants license for implementation as functions.
 \begin{note}
-The names defined as macros in C include the following:
+The names defined as macros in \IsoC{} include the following:
 \tcode{assert}, \tcode{offsetof}, \tcode{setjmp}, \tcode{va_arg},
 \tcode{va_end}, and \tcode{va_start}.
 \end{note}
 
 \pnum
-Names that are defined as functions in C shall be defined as functions in the
+Names that are defined as functions in \IsoC{} shall be defined as functions in the
 \Cpp{} standard library.
 \begin{footnote}
-This disallows the practice, allowed in C, of
+This disallows the practice, allowed in \IsoC{}, of
 providing a masking macro in addition to the function prototype. The only way to
 achieve equivalent inline behavior in \Cpp{} is to provide a definition as an
 extern inline function.
@@ -1320,7 +1320,7 @@
 \tcode{".h"} headers dump all their names into the global namespace, whereas the
 newer forms keep their names in namespace \tcode{std}. Therefore, the newer
 forms are the preferred forms for all uses except for \Cpp{} programs which are
-intended to be strictly compatible with C.
+intended to be strictly compatible with \IsoC{}.
 \end{footnote}
 
 \pnum
@@ -1455,7 +1455,7 @@
 It is unspecified to which module a declaration in the standard library
 is attached.
 \begin{note}
-Implementations are required to ensure that mixing
+Conforming implementations ensure that mixing
 \tcode{\#include} and \tcode{import} does not result in
 conflicting attachments\iref{basic.link}.
 \end{note}

source/templates.tex

@@ -6317,7 +6317,7 @@
 into the templated function, variable, or class
 are two declarations of the same entity.
 \begin{note}
-These declarations are required to have matching types as specified in~\ref{basic.link}, except as specified in~\ref{except.spec}.
+These declarations need to have matching types as specified in~\ref{basic.link}, except as specified in~\ref{except.spec}.
 \begin{example}
 \begin{codeblock}
 template<typename T> T var = {};
@@ -6367,7 +6367,7 @@
 
 \pnum
 \begin{note}
-An explicit instantiation of a constrained template is required
+An explicit instantiation of a constrained template needs
 to satisfy that template's associated constraints\iref{temp.constr.decl}.
 The satisfaction of constraints is determined
 % FIXME: What is a "template name"? Does this mean "simple-template-id"?
@@ -6514,10 +6514,9 @@
 An explicit specialization does not introduce a name\iref{basic.scope.scope}.
 A declaration of a function template, class template, or variable template being explicitly
 specialized shall be reachable from the declaration of
-the explicit
-specialization.
+the explicit specialization.
 \begin{note}
-A declaration, but not a definition of the template is required.
+A declaration, but not a definition of the template is needed.
 \end{note}
 The definition of a class or class template shall be reachable from the
 declaration of an explicit specialization for a member template of the class
@@ -6708,7 +6707,7 @@
 
 \pnum
 \begin{note}
-An explicit specialization of a constrained template is required
+An explicit specialization of a constrained template needs
 to satisfy that template's associated constraints\iref{temp.constr.decl}.
 The satisfaction of constraints is determined
 when forming the template name of an explicit specialization
@@ -7305,10 +7304,8 @@
 invalid type or expression is one that would be ill-formed, with a diagnostic
 required, if written in the same context using the substituted arguments.
 \begin{note}
-If no
-diagnostic is required, the program is still ill-formed. Access checking is done
-as part of the substitution
-process.
+If no diagnostic is required, the program is still ill-formed.
+Access checking is done as part of the substitution process.
 \end{note}
 Invalid types and expressions can result in a deduction failure
 only in the immediate context of the deduction substitution loci.

source/threads.tex

@@ -6305,8 +6305,8 @@
 \begin{note}
 After a thread \tcode{A} has called \tcode{unlock()}, releasing a mutex, it is possible for another
 thread \tcode{B} to lock the same mutex, observe that it is no longer in use, unlock it, and
-destroy it, before thread \tcode{A} appears to have returned from its unlock call. Implementations
-are required to handle such scenarios correctly, as long as thread \tcode{A} doesn't access the
+destroy it, before thread \tcode{A} appears to have returned from its unlock call. Conforming implementations
+handle such scenarios correctly, as long as thread \tcode{A} does not access the
 mutex after the unlock call returns. These cases typically occur when a reference-counted object
 contains a mutex that is used to protect the reference count.
 \end{note}

source/time.tex

@@ -7923,7 +7923,7 @@
 @\tcode{\placeholder{day}}@/@\tcode{\placeholder{month}}@/@\tcode{\placeholder{year}}@
 \end{codeblock}
 
-Anywhere a \tcode{\placeholder{day}} is required, any of the following can also be specified:
+Anywhere a \tcode{\placeholder{day}} is needed, any of the following can also be specified:
 
 \begin{codeblock}
 last

source/utilities.tex

@@ -3002,7 +3002,7 @@
 (or \tcode{u$_{\mathrm{tail}}$}) to be constructed. It might not
 even be possible, as \tcode{t} and \tcode{u} are not required to be copy
 constructible. Also, all comparison operator functions are short circuited;
-they do not perform element accesses beyond what is required to determine the
+they do not perform element accesses beyond what is needed to determine the
 result of the comparison.
 \end{note}