Improve layout for Literal Expressions section

framework-docs/modules/ROOT/pages/core/expressions/language-ref/literal.adoc

@@ -3,20 +3,22 @@
 
 SpEL supports the following types of literal expressions.
 
-- strings
-- numeric values: integer (`int` or `long`), hexadecimal (`int` or `long`), real (`float`
-  or `double`)
-- boolean values: `true` or `false`
-- null
-
-Strings can be delimited by single quotation marks (`'`) or double quotation marks (`"`). To
-include a single quotation mark within a string literal enclosed in single quotation
-marks, use two adjacent single quotation mark characters. Similarly, to include a double
-quotation mark within a string literal enclosed in double quotation marks, use two
-adjacent double quotation mark characters.
-
-Numbers support the use of the negative sign, exponential notation, and decimal points.
-By default, real numbers are parsed by using `Double.parseDouble()`.
+String ::
+  Strings can be delimited by single quotation marks (`'`) or double quotation marks
+  (`"`). To include a single quotation mark within a string literal enclosed in single
+  quotation marks, use two adjacent single quotation mark characters. Similarly, to
+  include a double quotation mark within a string literal enclosed in double quotation
+  marks, use two adjacent double quotation mark characters.
+Number ::
+  Numbers support the use of the negative sign, exponential notation, and decimal points.
+  * Integer: `int` or `long`
+  * Hexadecimal: `int` or `long`
+  * Real: `float` or `double`
+  ** By default, real numbers are parsed using `Double.parseDouble()`.
+Boolean ::
+  `true` or `false`
+Null ::
+  `null`
 
 The following listing shows simple usage of literals. Typically, they are not used in
 isolation like this but, rather, as part of a more complex expression -- for example,