Improve documentation of some functions

h2/src/docsrc/help/help.csv

@@ -4051,7 +4051,11 @@ CONCAT_WS(',', NAME, '!')
 DIFFERENCE(string, string)
 ","
 Returns the difference between the sounds of two strings.
-This method returns an int.
+The difference is calculated as a number of matched characters
+in the same positions in SOUNDEX representations of arguments.
+This method returns an int between 0 and 4 inclusive, or null if any of its parameters is null.
+Note that value of 0 means that strings are not similar to each other.
+Value of 4 means that strings are fully similar to each other (have the same SOUNDEX representation).
 ","
 DIFFERENCE(T1.NAME, T2.NAME)
 "
@@ -4263,8 +4267,8 @@ REPLACE(NAME, ' ')
 SOUNDEX(string)
 ","
 Returns a four character code representing the sound of a string.
-See also http://www.archives.gov/genealogy/census/soundex.html .
-This method returns a string.
+This method returns a string, or null if parameter is null.
+See https://en.wikipedia.org/wiki/Soundex for more information.
 ","
 SOUNDEX(NAME)
 "
@@ -4476,7 +4480,7 @@ The datetimeField indicates the unit.
 Only TIMEZONE_HOUR and TIMEZONE_MINUTE fields use the time zone offset component.
 With all other fields if date/time values have time zone offset component it is ignored.
 ","
-DATEDIFF('YEAR', T1.CREATED, T2.CREATED)
+DATEDIFF(YEAR, T1.CREATED, T2.CREATED)
 "
 
 "Functions (Time and Date)","DAYNAME","

h2/src/tools/org/h2/build/doc/dictionary.txt

@@ -799,4 +799,4 @@ mpg casted pzm mls constrained subtypes complains
 ranks rno dro rko precede cume reopens preceding unbounded rightly itr lag maximal tiles tile ntile signify
 partitioned tri
 
-discard enhancements nolock
+discard enhancements nolock surefire