Add more examples and explanations

Added some clarifying examples to sections on echo(), constants, and
cleaned up formatting on others. Added further explanation about the
spaceship operator.

php.html.markdown

@@ -104,7 +104,8 @@ END;
 echo 'This string ' . 'is concatenated';
 
 // Strings can be passed in as parameters to echo
-echo 'Multiple', 'Parameters', 'Valid';
+echo 'Multiple', 'Parameters', 'Valid';  // Returns 'MultipleParametersValid'
+
 
 /********************************
  * Constants
@@ -117,8 +118,10 @@ echo 'Multiple', 'Parameters', 'Valid';
 // followed by any number of letters, numbers, or underscores.
 define("FOO",     "something");
 
-// access to a constant is possible by direct using the choosen name
-echo 'This outputs '.FOO;
+// access to a constant is possible by calling the choosen name without a $
+echo FOO; // Returns 'something'
+echo 'This outputs '.FOO;  // Returns 'This ouputs something'
+
 
 
 /********************************
@@ -159,9 +162,9 @@ echo('Hello World!');
 
 print('Hello World!'); // The same as echo
 
-// echo is actually a language construct, so you can drop the parentheses.
+// echo and print are language constructs too, so you can drop the parentheses
 echo 'Hello World!';
-print 'Hello World!'; // So is print
+print 'Hello World!';
 
 $paragraph = 'paragraph';
 
@@ -219,7 +222,11 @@ assert($a !== $d);
 assert(1 === '1');
 assert(1 !== '1');
 
-// spaceship operator since PHP 7
+// 'Spaceship' operator (since PHP 7)
+// Returns 0 if values on either side are equal
+// Returns 1 if value on the left is greater
+// Returns -1 if the value on the right is greater
+
 $a = 100;
 $b = 1000;