Added a section about soft tabs and hard tabs

Author: mipo256

index.rst

@@ -60,6 +60,14 @@ In EditorConfig:
   settings based on the key-value pairs.
 - "Editors" permit editing files, and use plugins to update settings for
   files being edited.
+- The words "tab" and "hard tab" are assumed to be interchangable and to represent the 
+  character defined by the Unicode HT/TAB symbol (U+0009). 
+- The words "space" and "soft tab" are also assumed to be interchangable and to represent the
+  character defined by the Unicode Space/SP symbol (U+0020).
+- "Column" is an abstract atomic unit of indentation. A single space, as defined above,
+  is expected to contribute exactly one column to the indentation of a given line. The amount of 
+  columns contributed by the hard tab depends on the configuration pairs defined in the 
+  :ref:`_supported-pairs` section.
 
 A conforming core or plugin must pass the tests in the
 `core-tests repository`_ or `plugin-tests repository`_, respectively.
@@ -332,7 +340,7 @@ section to specify their behavior. Consider the following code snippet:
 
 The ``indent_size`` setting for this code snippet equals 4, because ``indent_size`` means how many columns are required
 to indent the next line in relation to previous (if indentation, of course, is applicable for this line). Then the next question
-is *how* this indentation of 4 columns is achieved. It may be 4 consequent spaces/soft tabs,
+is *how* this indentation of 4 columns is achieved. It may be 4 consequent spaces,
 a single tab with width equal to 4, or two tabs with width equal to 2.
 
 This is when ``indent_style`` comes into picture. It specifies what character should be used **whenever possible** in order to