diff --git a/Doc/library/stdtypes.rst b/Doc/library/stdtypes.rst
index f2563dd..1fb736b 100644
--- a/Doc/library/stdtypes.rst
+++ b/Doc/library/stdtypes.rst
@@ -898,20 +898,26 @@
 .. method:: str.isalnum()
 
    Return true if all characters in the string are alphanumeric and there is at
-   least one character, false otherwise.
+   least one character, false otherwise.  A character ``c`` is alphanumeric if one
+   of the following returns ``True``: ``c.isalpha()``, ``c.isdecimal()``,
+   ``c.isdigit()``, or ``c.isnumeric()``.
 
 
 .. method:: str.isalpha()
 
    Return true if all characters in the string are alphabetic and there is at least
-   one character, false otherwise.
+   one character, false otherwise.  Alphabetic characters are those characters defined
+   in the Unicode character database as "Letter", i.e., those with general category
+   property being one of "Lm", "Lt", "Lu", "Ll", or "Lo".  Note that this is different
+   from the "Alphabetic" property defined in the Unicode Standard.
 
 
 .. method:: str.isdecimal()
 
    Return true if all characters in the string are decimal
    characters and there is at least one character, false
-   otherwise. Decimal characters include digit characters, and all characters
+   otherwise. Decimal characters are those from general category "Nd". This category
+   includes digit characters, and all characters
    that that can be used to form decimal-radix numbers, e.g. U+0660,
    ARABIC-INDIC DIGIT ZERO.
 
@@ -919,7 +925,9 @@
 .. method:: str.isdigit()
 
    Return true if all characters in the string are digits and there is at least one
-   character, false otherwise.
+   character, false otherwise.  Digits include decimal characters and digits that need
+   special handling, such as the compatibility superscript digits.  Formally, a digit
+   is a character that has the property value Numeric_Type=Digit or Numeric_Type=Decimal.
 
 
 .. method:: str.isidentifier()
@@ -931,7 +939,9 @@
 .. method:: str.islower()
 
    Return true if all cased characters in the string are lowercase and there is at
-   least one cased character, false otherwise.
+   least one cased character, false otherwise.  Cased characters are those with
+   general category property being one of "Lu", "Ll", or "Lt" and lowercase characters
+   are those with general category property "Ll".
 
 
 .. method:: str.isnumeric()
@@ -940,7 +950,8 @@
    characters, and there is at least one character, false
    otherwise. Numeric characters include digit characters, and all characters
    that have the Unicode numeric value property, e.g. U+2155,
-   VULGAR FRACTION ONE FIFTH.
+   VULGAR FRACTION ONE FIFTH.  Formally, numeric characters are those with the property
+   value Numeric_Type=Digit, Numeric_Type=Decimal or Numeric_Type=Numeric.
 
 
 .. method:: str.isprintable()
@@ -957,8 +968,9 @@
 .. method:: str.isspace()
 
    Return true if there are only whitespace characters in the string and there is
-   at least one character, false otherwise.
-
+   at least one character, false otherwise.  Whitespace characters  are those
+   characters defined in the Unicode character database as "Other" or "Separator"
+   and those with bidirectional property being one of "WS", "B", or "S".
 
 .. method:: str.istitle()
 
@@ -970,7 +982,9 @@
 .. method:: str.isupper()
 
    Return true if all cased characters in the string are uppercase and there is at
-   least one cased character, false otherwise.
+   least one cased character, false otherwise. Cased characters are those with
+   general category property being one of "Lu", "Ll", or "Lt" and uppercase characters
+   are those with general category property "Lu".
 
 
 .. method:: str.join(iterable)