Improve description of range literal

syntax_and_semantics/literals/range.md

@@ -1,14 +1,32 @@
 # Range
 
-A [Range](http://crystal-lang.org/api/Range.html) is typically constructed with a range literal:
+A [Range](http://crystal-lang.org/api/Range.html) represents an interval between two values. It is typically constructed with a range literal, consisting of two or three dots:
 
-```crystal
-x..y  # an inclusive range, in mathematics: [x, y]
-x...y # an exclusive range, in mathematics: [x, y)
+* `x..y`: Two dots denote an inclusive range, including `x` and `y` and all values in between (in mathematics: `[x, y]`) .
+* `x...y`: Three dots denote an exclusive range, including `x` and all values up to but not including `y` (in mathematics: `[x, y)`).
 
-# Example:
+```cr
 (0..5).to_a # => [0, 1, 2, 3, 4, 5]
 (0...5).to_a # => [0, 1, 2, 3, 4]
 ```
 
+**NOTE:** Range literals are often wrapped in parentheses, for example if it is meant to be used as the receiver of a call. `0..5.to_a` without parentheses would be semantically equivalent to `0..(5.to_a)` because method calls and other operators have higher precedence than the range literal.
+
 An easy way to remember which one is inclusive and which one is exclusive it to think of the extra dot as if it pushes *y* further away, thus leaving it outside of the range.
+
+The literal `x..y` is semantically equivalent to the explicit constructor `Range.new(x, y)` and `x...y` to `Range.new(x, y, true)`.
+
+The begin and end values do not necessarily need to be of the same type: `true..1` is a valid range, although pretty useless `Enumerable` methods won't work with incompatible types. They need at least to be comparable.
+
+Ranges with `nil` as begin are called begin-less and `nil` as end are called end-less ranges. In the literal notation, `nil` can be omitted: `x..` is an end-less range starting from `x`, and `..x` is an begin-less range ending at `x`.
+
+```cr
+numbers = [1, 10, 3, 4, 5, 8]
+numbers.select(6..) # => [10, 8]
+numbers.select(..6) # => [1, 3, 4, 5]
+
+numbers[2..] = [3, 4, 5, 8]
+numbers[..2] = [1, 10, 3]
+```
+
+A range that is both begin-less and end-less is valid and can be expressed as `..` or `...` but it's typically not very useful.