Minor fix on parameters guide

Author: Acuadros95

_docs/tutorials/programming_rcl_rclc/parameters/parameters.md

@@ -5,26 +5,29 @@ permalink: /docs/tutorials/programming_rcl_rclc/parameters/
 
 <img src="https://img.shields.io/badge/Written_for-Galactic-green" style="display:inline"/> <img src="https://img.shields.io/badge/Tested_on-Rolling-green" style="display:inline"/>
 
-ROS 2 parameters allow the user to create variables on a node and manipulate/read them with different ROS2 commands. Further information about ROS 2 parameters can be found [here](https://docs.ros.org/en/galactic/Tutorials/Parameters/Understanding-ROS2-Parameters.html)
+ROS 2 parameters allow the user to create variables on a node and manipulate/read them with different ROS2 commands. Further information about ROS 2 parameters can be found [here](https://docs.ros.org/en/galactic/Tutorials/Parameters/Understanding-ROS2-Parameters.html). 
 
 Ready to use code related to this tutorial can be found in [`rclc/rclc_examples/src/example_parameter_server.c`](https://github.com/ros2/rclc/blob/master/rclc_examples/src/example_parameter_server.c). Fragments of code from this example is used on this tutorial.
 
 micro-ROS parameters implementation has been upgraded in the latest micro-ROS Rolling distribution, two approaches are presented in this tutorial: micro-ROS Foxy/Galactic and micro-ROS Rolling and beyond:
 
-- [Initialization](#initialization)
-- [Memory requirements](#memory-requirements)
-- [Add a parameter](#add-a-parameter)
-- [Cleaning up](#cleaning-up)
+- [General implementation](#general-implementation)
+  - [Initialization](#initialization)
+  - [Memory requirements](#memory-requirements)
+  - [Add a parameter](#add-a-parameter)
+  - [Cleaning up](#cleaning-up)
 - [micro-ROS Foxy/Galactic](#micro-ros-foxygalactic)
   - [Initialization options](#initialization-options)
   - [Callback](#callback)
 - [micro-ROS Rolling](#micro-ros-rolling)
   - [Initialization options](#initialization-options-1)
   - [Callback](#callback-1)
+  - [Add a parameter](#add-a-parameter-1)
   - [Delete a parameter](#delete-a-parameter)
   - [Parameters description](#parameters-description)
 
-## Initialization
+## General implementation
+### Initialization
 
 - Default initialization:
     ```c
@@ -35,16 +38,16 @@ micro-ROS parameters implementation has been upgraded in the latest micro-ROS Ro
     rcl_ret_t rc = rclc_parameter_server_init_default(&param_server, &node);
 
     if (RCL_RET_OK != rc) {
-    ... // Handle error
-    return -1;
+        ... // Handle error
+        return -1;
     }
     ```
 
-## Memory requirements
+### Memory requirements
 
 The parameter server uses 5 services and an optional publisher, this needs to be taken into account on the `rmw-microxredds` package memory configuration:
 
-```json
+```yaml
 # colcon.meta example with memory requirements to use a parameter server
 {
     "names": {
@@ -71,7 +74,7 @@ rc = rclc_executor_init(
     RCLC_PARAMETER_EXECUTOR_HANDLES_NUMBER, &allocator);
 ```
 
-## Add a parameter
+### Add a parameter
 
 micro-ROS parameter server supports the following parameter types:
 
@@ -90,8 +93,8 @@ micro-ROS parameter server supports the following parameter types:
     rc = rclc_parameter_get_bool(&param_server, "param1", &param_value);
 
     if (RCL_RET_OK != rc) {
-    ... // Handle error
-    return -1;
+        ... // Handle error
+        return -1;
     }
     ```
 
@@ -127,7 +130,7 @@ micro-ROS parameter server supports the following parameter types:
 
 *Max name size is controlled by the compilation time option `RCLC_PARAMETER_MAX_STRING_LENGTH`, default value is 50.*
 
-## Cleaning up
+### Cleaning up
 
 To destroy an initialized parameter server:
 
@@ -161,8 +164,8 @@ This will delete any automatically created infrastructure on the agent (if possi
     rcl_ret_t rc = rclc_parameter_server_init_with_option(&param_server, &node, &options);
 
     if (RCL_RET_OK != rc) {
-    ... // Handle error
-    return -1;
+        ... // Handle error
+        return -1;
     }
     ```
 
@@ -220,29 +223,30 @@ rc = rclc_executor_add_parameter_server(&executor, &param_server, NULL);
   - notify_changed_over_dds: Publish parameters events to the rest of nodes.
   - max_params: Maximum number of parameters allowed on the `rclc_parameter_server_t` object.
   - allow_undeclared_parameters: Allows creation of parameters from external parameters clients. A new parameter will be created if a `set` operation is requested on a non-existing parameter.
-  - low_mem_mode: Reduces the memory used by the parameter server, functionality constrains are applied.
+  - low_mem_mode: Reduces the memory used by the parameter server, functionality constrains are applied.  
 
-  ```c
-  // Parameter server object
-  rclc_parameter_server_t param_server;
+    ```c
+    // Parameter server object
+    rclc_parameter_server_t param_server;
 
-  // Initialize parameter server options
-  const rclc_parameter_options_t options = {
-      .notify_changed_over_dds = true,
-      .max_params = 4,
-      .allow_undeclared_parameters = true,
-      .low_mem_mode = false; };
+    // Initialize parameter server options
+    const rclc_parameter_options_t options = {
+        .notify_changed_over_dds = true,
+        .max_params = 4,
+        .allow_undeclared_parameters = true,
+        .low_mem_mode = false; };
 
-  // Initialize parameter server with configured options
-  rcl_ret_t rc = rclc_parameter_server_init_with_option(&param_server, &node, &options);
+    // Initialize parameter server with configured options
+    rcl_ret_t rc = rclc_parameter_server_init_with_option(&param_server, &node, &options);
 
-  if (RCL_RET_OK != rc) {
-  ... // Handle error
-  return -1;
-  }
-  ```
+    if (RCL_RET_OK != rc) {
+    ... // Handle error
+    return -1;
+    }
+    ```
 
 - Low memory mode:
+
     This mode ports the parameters functionality to memory constrained devices. The following constrains are applied:
     - Request size limited to 1 parameter on Set, Get, Get types and Describe services.
     - List parameters request has no prefixes enabled nor depth.
@@ -268,37 +272,44 @@ Callback parameters:
 ```c
 bool on_parameter_changed(const Parameter * old_param, const Parameter * new_param, void * context)
 {
-(void) context;
-
-if (old_param == NULL) {
-    printf("Creating new parameter %s\n", new_param->name.data);
-} else if (new_param == NULL) {
-    printf("Deleting parameter %s\n", old_param->name.data);
-} else {
-    printf("Parameter %s modified.", old_param->name.data);
-    switch (old_param->value.type) {
-    case RCLC_PARAMETER_BOOL:
-        printf(
-        " Old value: %d, New value: %d (bool)", old_param->value.bool_value,
-        new_param->value.bool_value);
-        break;
-    case RCLC_PARAMETER_INT:
-        printf(
-        " Old value: %ld, New value: %ld (int)", old_param->value.integer_value,
-        new_param->value.integer_value);
-        break;
-    case RCLC_PARAMETER_DOUBLE:
-        printf(
-        " Old value: %f, New value: %f (double)", old_param->value.double_value,
-        new_param->value.double_value);
-        break;
-    default:
-        break;
+    (void) context;
+
+    if (old_param == NULL)
+    {
+        printf("Creating new parameter %s\n", new_param->name.data);
     }
-    printf("\n");
-}
+    else if (new_param == NULL)
+    {
+        printf("Deleting parameter %s\n", old_param->name.data);
+    }
+    else
+    {
+        printf("Parameter %s modified.", old_param->name.data);
+        switch (old_param->value.type)
+        {
+            case RCLC_PARAMETER_BOOL:
+                printf(
+                " Old value: %d, New value: %d (bool)", old_param->value.bool_value,
+                new_param->value.bool_value);
+                break;
+            case RCLC_PARAMETER_INT:
+                printf(
+                " Old value: %ld, New value: %ld (int)", old_param->value.integer_value,
+                new_param->value.integer_value);
+                break;
+            case RCLC_PARAMETER_DOUBLE:
+                printf(
+                " Old value: %f, New value: %f (double)", old_param->value.double_value,
+                new_param->value.double_value);
+                break;
+            default:
+                break;
+        }
 
-return true;
+        printf("\n");
+    }
+
+    return true;
 }
 ```
 
@@ -312,7 +323,6 @@ Parameters modifications are disabled while this callback is executed, causing t
 - rclc_add_parameter_constraints_double
 - rclc_add_parameter_constraints_integer
 
-
 Once the parameter server and the executor are initialized, the parameter server must be added to the executor in order to accept parameters commands from ROS2:
 ```c
 // Add parameter server to executor including defined callback
@@ -331,51 +341,51 @@ To configure the callback context:
 rc = rclc_executor_add_parameter_server_with_context(&executor, &param_server, on_parameter_changed, &context);
 ```
 
+### Add a parameter
+Parameters can also be created by external clients if `allow_undeclared_parameters` flag is set.
+They client just needs to set a value on a unexisting parameter, the parameter will be created if the server is not full and the callback allows the operation.
+
 ### Delete a parameter
 Parameters can be deleted both by the parameter server and external clients:
-Example usage:
 ```c
 rclc_delete_parameter(&param_server, "param2");
 ```
 
-Note that for external delete requests the server callback will be executed, allowing the user to reject the operation.
+*For external delete requests the server callback will be executed, allowing the user to reject the operation.*
 
 ### Parameters description
 
-- Parameter description
-    Adds a description of a parameter and its constrains. This descriptors will be returned to describe parameters requests.
-    Example usage:
+- Parameter description  
+    Adds a description of a parameter and its constrains, which will be returned on a describe parameters requests:
     ```c
     rclc_add_parameter_description(&param_server, "param2", "Second parameter", "Only even numbers");
     ```
 
     *The maximum string size is controlled by the compilation time option `RCLC_PARAMETER_MAX_STRING_LENGTH`, default value is 50.*
 
-- Parameter constrains
-    Informative numeric constrains can be added to int and double parameters, returning this values on describe parameters requests.
-    Note that this constrains will not be applied by the parameter server, leaving values filtering to the user callback.
-
-    The following values can be configured:
+- Parameter constrains  
+    Informative numeric constrains can be added to int and double parameters, returning this values on describe parameters requests:
     - from_value: Start value for valid values, inclusive.
     - to_value: End value for valid values, inclusive.
     - step: Size of valid steps between the from and to bound.
 
-    Example usage:
-    ```c
-    int64_t int_from = 0;
-    int64_t int_to = 20;
-    uint64_t int_step = 2;
-    rclc_add_parameter_constraints_integer(&param_server, "param2", int_from, int_to, int_step);
-
-    double double_from = -0.5;
-    double double_to = 0.5;
-    double double_step = 0.01;
-    rclc_add_parameter_constraints_double(&param_server, "param3", double_from, double_to, double_step);
-    ```
+        ```c
+        int64_t int_from = 0;
+        int64_t int_to = 20;
+        uint64_t int_step = 2;
+        rclc_add_parameter_constraints_integer(&param_server, "param2", int_from, int_to, int_step);
+
+        double double_from = -0.5;
+        double double_to = 0.5;
+        double double_step = 0.01;
+        rclc_add_parameter_constraints_double(&param_server, "param3", double_from, double_to, double_step);
+        ```
 
-- Read only parameters:
-    The new API offers a read only flag. This flag blocks parameter changes from external clients, but allows changes on the server side. Example usage:
+    *This constrains will not be applied by the parameter server, leaving values filtering to the user callback.*
+
+- Read only parameters:  
+    The new API offers a read only flag. This flag blocks parameter changes from external clients, but allows changes on the server side:
     ```c
     bool read_only = true;
     rclc_set_parameter_read_only(&param_server, "param3", read_only);
-    ```
+    ```