[DOC] Tweaks for String#index

1 files changed, 18 insertions, 14 deletions

diff --git a/doc/string/index.rdoc b/doc/string/index.rdoc
index ce09a37bdf..cc34bc68e6 100644
--- a/doc/string/index.rdoc
+++ b/doc/string/index.rdoc
@@ -1,31 +1,35 @@
-Returns the integer index of the first match for the given argument,
-or +nil+ if none found;
-the search of +self+ is forward, and begins at position +offset+ (in characters).
+Returns the integer position of the first substring that matches the given argument +pattern+,
+or +nil+ if none found.
 
-With string argument +substring+,
+When +pattern+ is a string,
 returns the index of the first matching substring in +self+:
 
   'foo'.index('f')         # => 0
   'foo'.index('o')         # => 1
   'foo'.index('oo')        # => 1
   'foo'.index('ooo')       # => nil
-  'тест'.index('с')        # => 2
-  'こんにちは'.index('ち')   # => 3
+  'тест'.index('с')        # => 2  # Characters, not bytes.
+  'こんにちは'.index('ち')  # => 3
 
-With Regexp argument +regexp+, returns the index of the first match in +self+:
+When +pattern is a Regexp, returns the index of the first match in +self+:
 
   'foo'.index(/o./) # => 1
   'foo'.index(/.o/) # => 0
 
-With positive integer +offset+, begins the search at position +offset+:
+When +offset+ is non-negative, begins the search at position +offset+;
+the returned index is relative to the beginning of +self+:
 
-  'foo'.index('o', 1)        # => 1
-  'foo'.index('o', 2)        # => 2
-  'foo'.index('o', 3)        # => nil
+  'bar'.index('r', 0)        # => 2
+  'bar'.index('r', 1)        # => 2
+  'bar'.index('r', 2)        # => 2
+  'bar'.index('r', 3)        # => nil
+  'bar'.index(/[r-z]/, 0)    # => 2
   'тест'.index('с', 1)       # => 2
-  'こんにちは'.index('ち', 2)  # => 3
+  'тест'.index('с', 2)       # => 2
+  'тест'.index('с', 3)       # => nil  # Offset in characters, not bytes.
+  'こんにちは'.index('ち', 2) # => 3
 
-With negative integer +offset+, selects the search position by counting backward
+With negative integer argument +offset+, selects the search position by counting backward
 from the end of +self+:
 
   'foo'.index('o', -1)  # => 2
@@ -35,4 +39,4 @@ from the end of +self+:
   'foo'.index(/o./, -2) # => 1
   'foo'.index(/.o/, -2) # => 1
 
-Related: String#rindex.
+Related: see {Querying}[rdoc-ref:String@Querying].