double-check again

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/CallMethodViaReflection.scala

@@ -47,8 +47,8 @@ import org.apache.spark.util.Utils
   usage = "_FUNC_(class, method[, arg1[, arg2 ..]]) - Calls method with reflection.",
   extended = """
     Arguments:
-      class - a string literal that represents full-qualified class name.
-      method - a string literal that represents method name.
+      class - a string literal that represents a fully-qualified class name.
+      method - a string literal that represents a method name.
       arg - a string literal that represents arguments for the method.
 
     Examples:

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Cast.scala

@@ -114,11 +114,11 @@ object Cast {
 
 /** Cast the child expression to the target data type. */
 @ExpressionDescription(
-  usage = "_FUNC_(expr AS type) - Casts value expr to the target data type.",
+  usage = "_FUNC_(expr AS type) - Casts the value expr to the target data type.",
   extended = """
     Arguments:
       expr - an expression of any type.
-      type - data type.
+      type - data type to cast expr into.
 
     Examples:
       > SELECT _FUNC_('10' as int);

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/aggregate/ApproximatePercentile.scala

@@ -56,13 +56,15 @@ import org.apache.spark.sql.types._
       controls approximation accuracy at the cost of memory. Higher value of `accuracy` yields
       better accuracy, `1.0/accuracy` is the relative error of the approximation.
       When percentage is an array, each value of the percentage array must be between 0.0 and 1.0.
+      In this case, returns the approximate percentile array of column `col` at the given
+      percentage array.
   """,
   extended = """
     Arguments:
       col - a numeric expression.
       percentage - a numeric literal or an array literal of numeric type that defines the
-        percentile. For example, 0.5 means 50-percentile.
-      accuracy - a numeric literal.
+        percentile between 0.0 and 1.0. For example, 0.5 means 50-percentile.
+      accuracy - a numeric literal of approximation accuracy.
 
     Examples:
       > SELECT percentile_approx(10.0, array(0.5, 0.4, 0.1), 100);

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/aggregate/First.scala

@@ -30,7 +30,7 @@ import org.apache.spark.sql.types._
  */
 @ExpressionDescription(
   usage = """
-    _FUNC_(expr[, isIgnoreNull]) - Returns the first value of expr for a group of rows.
+    _FUNC_(expr[, isIgnoreNull]) - Returns the first value of `expr` for a group of rows.
       If isIgnoreNull is true, returns only non-null values.
   """,
   extended = """

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/aggregate/Last.scala

@@ -30,7 +30,7 @@ import org.apache.spark.sql.types._
  */
 @ExpressionDescription(
   usage = """
-    _FUNC_(expr[, isIgnoreNull]) - Returns the last value of expr for a group of rows.
+    _FUNC_(expr[, isIgnoreNull]) - Returns the last value of `expr` for a group of rows.
       If isIgnoreNull is true, returns only non-null values.
   """,
   extended = """

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/complexTypeCreator.scala

@@ -438,7 +438,7 @@ case class CreateNamedStructUnsafe(children: Seq[Expression]) extends Expression
     Arguments:
       text - a string expression that represents data to convert into map.
       pairDelim - a string literal that defines the delimiter to separate each pair. For example, ",".
-      keyValueDelim - a string literal that defines the delimiter to separate key and value in the pair. For example, ":".
+      keyValueDelim - a string literal that defines the delimiter to separate the key and value in the pair. For example, ":".
 
     Examples:
      > SELECT _FUNC_('a:1,b:2,c:3', ',', ':');

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/conditionalExpressions.scala

@@ -26,16 +26,14 @@ import org.apache.spark.sql.types._
 @ExpressionDescription(
   usage = "_FUNC_(expr1, expr2, expr3) - If expr1 is TRUE then IF() returns expr2; otherwise it returns expr3.",
   extended = """
-    _FUNC_(expr1, expr2, expr3)
-
-      Arguments:
-        expr1 - a boolean expression.
-        expr2 - an expression of any type that represents the return value when expr1 is TRUE.
-        expr3 - an expression of any type that represents the return value when expr1 is FALSE.
-
-      Examples:
-        > SELECT _FUNC_(1 < 2, 'a', 'b');
-         a
+    Arguments:
+      expr1 - a boolean expression.
+      expr2 - an expression of any type that represents the return value when expr1 is TRUE.
+      expr3 - an expression of any type that represents the return value when expr1 is FALSE.
+
+    Examples:
+      > SELECT _FUNC_(1 < 2, 'a', 'b');
+       a
   """)
 // scalastyle:on line.size.limit
 case class If(predicate: Expression, trueValue: Expression, falseValue: Expression)

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/datetimeExpressions.scala

@@ -400,11 +400,11 @@ case class WeekOfYear(child: Expression) extends UnaryExpression with ImplicitCa
 
 // scalastyle:off line.size.limit
 @ExpressionDescription(
-  usage = "_FUNC_(timestamp, fmt) - Converts expr to a value of string in the format specified by the date format fmt.",
+  usage = "_FUNC_(timestamp, fmt) - Converts timestamp to a value of string in the format specified by the date format fmt.",
   extended = """
     Arguments:
       timestamp - a timestamp expression.
-      fmt - string type expression that represents date/timestamp format used in java.text.SimpleDateFormat.
+      fmt - string type expression that represents the date/timestamp format available in java.text.SimpleDateFormat.
 
     Examples:
       > SELECT _FUNC_('2016-04-08', 'y');
@@ -443,7 +443,7 @@ case class DateFormatClass(left: Expression, right: Expression) extends BinaryEx
   extended = """
     Arguments:
       expr - a date, string or timestamp expression.
-      pattern - a string expression that represents date/timestamp format used in
+      pattern - a string expression that represents the date/timestamp format available in
         java.text.SimpleDateFormat.
 
     Examples:
@@ -476,7 +476,7 @@ case class ToUnixTimestamp(timeExp: Expression, format: Expression) extends Unix
   extended = """
     Arguments:
       expr - a date, string or timestamp expression.
-      pattern - a string expression that represents date/timestamp format used in
+      pattern - a string expression that represents the date/timestamp format available in
         java.text.SimpleDateFormat.
 
     Examples:
@@ -613,7 +613,7 @@ abstract class UnixTime extends BinaryExpression with ExpectsInputTypes {
   extended = """
     Arguments:
       unix_time - a numeric expression.
-      format - a string expression that represents date/timestamp format used in
+      format - a string expression that represents the date/timestamp format available in
         java.text.SimpleDateFormat.
 
     Examples:
@@ -846,7 +846,7 @@ case class TimeAdd(start: Expression, interval: Expression)
   extended = """
     Arguments:
       timestamp - a timestamp expression.
-      timezone - a string expression that represents time zone (e.g., 'Asia/Seoul').
+      timezone - a string expression that represents time zone. For example, 'Asia/Seoul'.
 
     Examples:
       > SELECT from_utc_timestamp('2016-08-31', 'Asia/Seoul');
@@ -970,7 +970,7 @@ case class AddMonths(startDate: Expression, numMonths: Expression)
  */
 // scalastyle:off line.size.limit
 @ExpressionDescription(
-  usage = "_FUNC_(timestamp1, timestamp2) - Returns number of months between dates expr1 and expr2.",
+  usage = "_FUNC_(timestamp1, timestamp2) - Returns number of months between dates timestamp1 and timestamp2.",
   extended = """
     Arguments:
       timestamp1 - a timestamp expression.
@@ -1014,7 +1014,7 @@ case class MonthsBetween(date1: Expression, date2: Expression)
   extended = """
     Arguments:
       timestamp - a timestamp expression.
-      timezone - a string expression that represents time zone (e.g., 'Asia/Seoul').
+      timezone - a string expression that represents time zone. For example, 'Asia/Seoul'.
 
     Examples:
       > SELECT _FUNC_('2016-08-31', 'Asia/Seoul');
@@ -1070,7 +1070,7 @@ case class ToUTCTimestamp(left: Expression, right: Expression)
  * Returns the date part of a timestamp or string.
  */
 @ExpressionDescription(
-  usage = "_FUNC_(date) - Extracts the date part of the date or datetime expression expr.",
+  usage = "_FUNC_(date) - Extracts the date part of the date or timestamp expression.",
   extended = """
     Arguments:
       date - a date expression.
@@ -1184,7 +1184,7 @@ case class TruncDate(date: Expression, format: Expression)
  * Returns the number of days from startDate to endDate.
  */
 @ExpressionDescription(
-  usage = "_FUNC_(date1, date2) - Returns the number of days between expr1 and expr2.",
+  usage = "_FUNC_(date1, date2) - Returns the number of days between date1 and date2.",
   extended = """
     Arguments:
       date1 - a date expression.

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/regexpExpressions.scala

@@ -72,7 +72,7 @@ trait StringRegexExpression extends ImplicitCastInputTypes {
   extended = """
     Arguments:
       str - a string expression.
-      pattern - a string expression.
+      pattern - a string expression that defines a regular expression pattern.
   """)
 case class Like(left: Expression, right: Expression)
   extends BinaryExpression with StringRegexExpression {
@@ -130,7 +130,7 @@ case class Like(left: Expression, right: Expression)
   extended = """
     Arguments:
       str - a string expression.
-      regexp - a string expression.
+      regexp - a string expression that defines a regular expression pattern.
   """)
 case class RLike(left: Expression, right: Expression)
   extends BinaryExpression with StringRegexExpression {
@@ -189,7 +189,7 @@ case class RLike(left: Expression, right: Expression)
   extended = """
     Arguments:
       str - a string expression.
-      regex - a string expression.
+      regex - a string expression that defines a regular expression pattern.
 
     Examples:
       > SELECT _FUNC_('oneAtwoBthreeC', '[ABC]');
@@ -229,8 +229,8 @@ case class StringSplit(str: Expression, pattern: Expression)
   extended = """
     Arguments:
       str - a string expression.
-      regexp - a string expression.
-      rep - a string expression.
+      regexp - a string expression that defines a regular expression pattern.
+      rep - a string expression that defines the replacement.
 
     Examples:
       > SELECT _FUNC_('100-200', '(\d+)', 'num');
@@ -340,7 +340,7 @@ case class RegExpReplace(subject: Expression, regexp: Expression, rep: Expressio
   extended = """
     Arguments:
       str - a string expression.
-      regexp - a string expression.
+      regexp - a string expression that defines a regular expression pattern.
       idx - a numeric expression that defines the index of a capturing group in regexp.
 
     Examples: