📝 document less-than comparability

doc/mkdocs/docs/api/basic_json/at.md

@@ -23,8 +23,8 @@ const_reference at(const json_pointer& ptr) const;
 ## Template parameters
 
 `KeyT`
-:   A type for an object key other than `basic_json::json_pointer`. This can also be a string literal or a string view
-    (C++17).
+:   A type for an object key other than `basic_json::json_pointer` that is less-than comparable with `string_t`. This
+    can also be a string literal or a string view (C++17).
 
 ## Parameters
 

doc/mkdocs/docs/api/basic_json/contains.md

@@ -11,8 +11,8 @@ value is not an object, `#!cpp false` is returned.
 ## Template parameters
 
 `KeyT`
-:   A type for an object key other than `basic_json::json_pointer`. This can also be a string literal or a string view 
-    (C++17).
+:   A type for an object key other than `basic_json::json_pointer` that is less-than comparable with `string_t`. This
+    can also be a string literal or a string view (C++17).
 
 ## Parameters
 

doc/mkdocs/docs/api/basic_json/count.md

@@ -11,7 +11,8 @@ always be `0` (`key` was not found) or `1` (`key` was found).
 ## Template parameters
 
 `KeyT`
-:   A type for an object key. This can also be a string literal or a string view (C++17).
+:   A type for an object key that is less-than comparable with `string_t`. This can also be a string literal or a string
+    view (C++17).
 
 ## Parameters
 

doc/mkdocs/docs/api/basic_json/erase.md

@@ -35,7 +35,8 @@ void erase(const size_type idx);
 ## Template parameters
 
 `KeyT`
-:   A type convertible to an object key. This can also be a string literal or a string view (C++17).
+:   A type for an object key that is less-than comparable with `string_t`. This can also be a string literal or a string
+    view (C++17).
 
 ## Parameters
 

doc/mkdocs/docs/api/basic_json/find.md

@@ -14,7 +14,8 @@ object, `end()` is returned.
 ## Template parameters
 
 `KeyT`
-:   A type for an object key. This can also be a string literal or a string view (C++17).
+:   A type for an object key that is less-than comparable with `string_t`. This can also be a string literal or a string
+    view (C++17).
 
 ## Parameters
 

doc/mkdocs/docs/api/basic_json/operator[].md

@@ -23,8 +23,8 @@ const_reference operator[](const json_pointer& ptr) const;
 ## Template parameters
 
 `KeyT`
-:   A type for an object key other than `basic_json::json_pointer`. This can also be a string literal or a string view
-    (C++17).
+:   A type for an object key other than `basic_json::json_pointer` that is less-than comparable with `string_t`. This
+    can also be a string literal or a string view (C++17).
 
 ## Parameters
 

doc/mkdocs/docs/api/basic_json/value.md

@@ -42,7 +42,8 @@ Unlike [`operator[]`](operator[].md), this function does not implicitly add an e
 ## Template parameters
 
 `KeyType`
-:   A type for an object key. This can also be a string literal or a string view (C++17).
+:   A type for an object key that is less-than comparable with `string_t`. This can also be a string literal or a string
+    view (C++17).
 `ValueType` 
 :   type compatible to JSON values, for instance `#!cpp int` for JSON integer numbers, `#!cpp bool` for JSON booleans,
     or `#!cpp std::vector` types for JSON arrays. Note the type of the expected value at `key`/`ptr` and the default