Better wording.

Co-authored-by: Hynek Schlawack <[email protected]>

Author: Julian

README.rst

@@ -105,7 +105,8 @@ They can be used when installing in order to include additional dependencies, e.
 
     $ pip install jsonschema'[format]'
 
-You will also want to read the `format validation documentation <https://python-jsonschema.readthedocs.io/en/latest/validate/#validating-formats>`_.
+Be aware that the mere presence of these dependencies – or even the specification of ``format`` checks in a schema – do **not** activate format checks (as per specification).
+Please read the `format validation documentation <https://python-jsonschema.readthedocs.io/en/latest/validate/#validating-formats>`_ for details.
 
 .. start cut from PyPI
 

docs/validate.rst

@@ -173,7 +173,8 @@ Validating Formats
 ------------------
 
 JSON Schema defines the :kw:`format` keyword which can be used to check if primitive types (``string``\s, ``number``\s, ``boolean``\s) conform to well-defined formats.
-By default, as per the specification, no validation is enforced. Optionally however, validation can be enabled by hooking a `format-checking object <jsonschema.FormatChecker>` into a `Validator`.
+By default, as per the specification, no validation is enforced.
+Optionally however, validation can be enabled by hooking a `format-checking object <jsonschema.FormatChecker>` into a `Validator`.
 
 .. doctest::