Enhance Boolean argument handling docs.

pekkaklarck · pekkaklarck · commit fc724b62270d · 2019-04-11T14:53:12.000+03:00
- Documentation in UG was outdated.
- Small enhancement also to BuiltIn doc.
diff --git a/doc/userguide/src/Appendices/BooleanArguments.rst b/doc/userguide/src/Appendices/BooleanArguments.rst
@@ -3,18 +3,14 @@ Boolean arguments
 
 Many keywords in Robot Framework `standard libraries`_ accept arguments that
 are handled as Boolean values true or false. If such an argument is given as
-a string, it is considered false if it is either empty or case-insensitively
-equal to `false` or `no`. Other strings are considered true regardless
-their value, and other argument types are tested using same `rules as in
-Python`__.
+a string, it is considered false if it is an empty string or equal to
+`FALSE`, `NONE`, `NO`, `OFF` or `0`, case-insensitively. Other
+strings are considered true unless the keyword documentation explicitly
+states otherwise, and other argument types are tested using the same
+`rules as in Python`__.
 
 __ http://docs.python.org/library/stdtypes.html#truth-value-testing
 
-Keyword can also accept other special strings than `false` and `no` that are
-to be considered false. For example, BuiltIn_ keyword `Should Be True` used
-in the examples below considers string `no values` given to its `values`
-argument as false.
-
 .. sourcecode:: robotframework
 
    *** Keywords ***
@@ -29,8 +25,7 @@ argument as false.
        Should Be Equal    ${x}    ${y}    Custom error    values=no           # Also string `no` is false.
        Should Be Equal    ${x}    ${y}    Custom error    values=${EMPTY}     # Empty string is false.
        Should Be Equal    ${x}    ${y}    Custom error    values=${FALSE}     # Python `False` is false.
-       Should Be Equal    ${x}    ${y}    Custom error    values=no values    # Special false string in this context.
+       Should Be Equal    ${x}    ${y}    Custom error    values=no values    # Special false string with this keyword.
 
-Note that prior to Robot Framework 2.9 handling Boolean arguments was
-inconsistent. Some keywords followed the above rules, but others simply
-considered all non-empty strings, including `false` and `no`, to be true.
+.. note:: Considering string `NONE` false is new in Robot Framework 3.0.3 and
+          considering also `OFF` and `0` false is new in Robot Framework 3.1.
diff --git a/src/robot/libraries/BuiltIn.py b/src/robot/libraries/BuiltIn.py
@@ -3345,8 +3345,9 @@ class BuiltIn(_Verify, _Converter, _Variables, _RunKeyword, _Control, _Misc):
     it is an empty string or equal to ``FALSE``, ``NONE``, ``NO``, ``OFF`` or
     ``0``, case-insensitively. Keywords verifying something that allow dropping
     actual and expected values from the possible error message also consider
-    string ``no values`` to be false. Other strings are considered true
-    regardless their value, and other argument types are tested using the same
+    string ``no values`` to be false. Other strings are considered true unless
+    the keyword documentation explicitly states otherwise, and other argument
+    types are tested using the same
     [http://docs.python.org/library/stdtypes.html#truth|rules as in Python].
 
     True examples:
