Update documentation

Author: evgeniums

docs/index.md

@@ -113,7 +113,7 @@ Basic usage of the library includes a few steps:
 - then, apply the [validator](#validator) to [object](#object) that must be validated;
 - finally, check the results and print [report](#report) if applicable.
 
-The library is suitable for both *post-validation* and *pre-validation*. *Post-validation* stands for validating the object that is already populated with the data. [*Pre-validation*](#single-member-adapter) stands for validating the data before writing it to the object. The same validator declaration can be used in both cases.
+The library is suitable for both *post-validation* and *pre-validation*. *Post-validation* stands for validating the object that is already populated with the data. *Pre-validation* stands for validating the data before writing it to the object. The same validator declaration can be used in both cases.
 
 # Definitions
 
@@ -150,6 +150,14 @@ Variable or value used as a validation sample in [operator](#operator).
 ##### *Operator*
 Atomic validation condition.
 
+##### *Post-validation*
+
+Validating the object that is already populated with the data.
+
+##### *Pre-validation*
+
+Validating the data before writing it to the object.
+
 ##### *Property*
 Method or member variable of C++ class or structure that must be validated, see [Properties](#properties).
 
@@ -1500,7 +1508,7 @@ There are three built-in adapter types implemented in `cpp-validator` library:
 
 ### Single member adapter
 
-*Single member adapter* validates only a single member. This adapter is best suitable for *pre-validation*, i.e. validating the data before updating an object in the object's setters. *Single member adapter* is constructed by calling `make_single_member_adapter()` helper that can have one of the following signatures:
+*Single member adapter* validates only a single member. This adapter is best suitable for [pre-validation](#pre-validation). *Single member adapter* is constructed by calling `make_single_member_adapter()` helper that can have one of the following signatures:
 - `make_single_member_adapter(member_path,val,reporter)` where
     - `member_path` is a [member](#member) specified in [member notation](#member-notation);
     - `val` is a variable to validate;