:memo: add more API documentation

doc/docset/docSet.sql

diff --git a/doc/docset/docSet.sql b/doc/docset/docSet.sql
index 93fd478..500de59 100644
--- a/doc/docset/docSet.sql
+++ b/doc/docset/docSet.sql
@@ -79,7 +79,9 @@
 INSERT INTO searchIndex(name, type, path) VALUES ('operator=', 'Operator', 'api/basic_json/operator=/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('operator==', 'Operator', 'api/basic_json/operator==/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('operator<', 'Operator', 'api/basic_json/operator</index.html');
+INSERT INTO searchIndex(name, type, path) VALUES ('operator<=', 'Operator', 'api/basic_json/operator<=/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('operator>', 'Operator', 'api/basic_json/operator>/index.html');
+INSERT INTO searchIndex(name, type, path) VALUES ('operator>=', 'Operator', 'api/basic_json/operator>=/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('operator[]', 'Operator', 'api/basic_json/operator[]/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('operator""_json', 'Literal', 'api/basic_json/operator_literal_json/index.html');
 INSERT INTO searchIndex(name, type, path) VALUES ('operator""_json_pointer', 'Literal', 'api/basic_json/operator_literal_json_pointer/index.html');

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

diff --git a/doc/mkdocs/docs/api/basic_json/index.md b/doc/mkdocs/docs/api/basic_json/index.md
index ff00525..cccb5d4 100644
--- a/doc/mkdocs/docs/api/basic_json/index.md
+++ b/doc/mkdocs/docs/api/basic_json/index.md
@@ -194,9 +194,9 @@
 - [**operator==**](operator==.md) - comparison: equal
 - [**operator!=**](operator!=.md) - comparison: not equal
 - [**operator<**](operator<.md) - comparison: less than
-- operator<= - comparison: less than or equal
+- [**operator<=**](operator<=.md) - comparison: less than or equal
 - [**operator>**](operator>.md) - comparison: greater than
-- operator>= - comparison: greater than or equal
+- [**operator>=**](operator>=.md) - comparison: greater than or equal
 
 ### Serialization
 

"b/doc/mkdocs/docs/api/basic_json/operator\074=.md"

diff --git "a/doc/mkdocs/docs/api/basic_json/operator\074=.md" "b/doc/mkdocs/docs/api/basic_json/operator\074=.md"
new file mode 100644
index 0000000..452ee49
--- /dev/null
+++ "b/doc/mkdocs/docs/api/basic_json/operator\074=.md"
@@ -0,0 +1,59 @@
+# basic_json::operator<=
+
+```cpp
+bool operator<=(const_reference lhs, const_reference rhs) noexcept,
+
+template<typename ScalarType>
+bool operator<=(const_reference lhs, const ScalarType rhs) noexcept;
+
+template<typename ScalarType>
+bool operator<=(ScalarType lhs, const const_reference rhs) noexcept;
+```
+
+Compares whether one JSON value `lhs` is less than or equal to another JSON value `rhs` by calculating
+`#cpp !(rhs < lhs)`.
+
+## Template parameters
+
+`ScalarType`
+:   a scalar type according to `std::is_scalar<ScalarType>::value`
+
+## Parameters
+
+`lhs` (in)
+:   first value to consider 
+
+`rhs` (in)
+:   second value to consider 
+
+## Return value
+
+whether `lhs` is less than or equal to `rhs`
+
+## Exception safety
+
+No-throw guarantee: this function never throws exceptions.
+
+## Complexity
+
+Linear.
+
+## Example
+
+??? example
+
+    The example demonstrates comparing several JSON types.
+        
+    ```cpp
+    --8<-- "examples/operator__lessequal.cpp"
+    ```
+    
+    Output:
+    
+    ```json
+    --8<-- "examples/operator__lessequal.output"
+    ```
+
+## Version history
+
+- Added in version 1.0.0.

"b/doc/mkdocs/docs/api/basic_json/operator\076=.md"

diff --git "a/doc/mkdocs/docs/api/basic_json/operator\076=.md" "b/doc/mkdocs/docs/api/basic_json/operator\076=.md"
new file mode 100644
index 0000000..19834c0
--- /dev/null
+++ "b/doc/mkdocs/docs/api/basic_json/operator\076=.md"
@@ -0,0 +1,59 @@
+# basic_json::operator>=
+
+```cpp
+bool operator>=(const_reference lhs, const_reference rhs) noexcept,
+
+template<typename ScalarType>
+bool operator>=(const_reference lhs, const ScalarType rhs) noexcept;
+
+template<typename ScalarType>
+bool operator>=(ScalarType lhs, const const_reference rhs) noexcept;
+```
+
+Compares whether one JSON value `lhs` is greater than or equal to another JSON value `rhs` by calculating
+`#!cpp !(lhs < rhs)`.
+
+## Template parameters
+
+`ScalarType`
+:   a scalar type according to `std::is_scalar<ScalarType>::value`
+
+## Parameters
+
+`lhs` (in)
+:   first value to consider 
+
+`rhs` (in)
+:   second value to consider 
+
+## Return value
+
+whether `lhs` is less than or equal to `rhs`
+
+## Exception safety
+
+No-throw guarantee: this function never throws exceptions.
+
+## Complexity
+
+Linear.
+
+## Example
+
+??? example
+
+    The example demonstrates comparing several JSON types.
+        
+    ```cpp
+    --8<-- "examples/operator__greaterequal.cpp"
+    ```
+    
+    Output:
+    
+    ```json
+    --8<-- "examples/operator__greaterequal.output"
+    ```
+
+## Version history
+
+- Added in version 1.0.0.

doc/mkdocs/mkdocs.yml

diff --git a/doc/mkdocs/mkdocs.yml b/doc/mkdocs/mkdocs.yml
index 272ee5f..1bc365d 100644
--- a/doc/mkdocs/mkdocs.yml
+++ b/doc/mkdocs/mkdocs.yml
@@ -147,7 +147,9 @@
         - api/basic_json/operator==.md
         - api/basic_json/operator!=.md
         - api/basic_json/operator<.md
+        - api/basic_json/operator<=.md
         - api/basic_json/operator>.md
+        - api/basic_json/operator>=.md
         - api/basic_json/operator+=.md
         - api/basic_json/operator_literal_json.md
         - api/basic_json/operator_literal_json_pointer.md