Php post/pre increment/decrement, precedence -

As I know, preincrement is calculated before all other functions, calculating post-progression after all operations She goes.

In PHP documents it is said that there is a lot of priority in growth (as I consider to be a pre-pay increase), post-arrangement should have very little priority, in fact, the lowest one

+ operator priority is too high then ++ one (according to the docs).

So, now the question is: An example in Php docs, which indicates that preference and postcure may vary in an expression:

  // mix ++ and + Undefined behavior produces $ a = 1; Resonance ++ $ a + $ a ++; // 4 or 5 can print   
 Why? WTF? I look at the following scenario, it is very clear:  
 
 Calculate the sum for $ ainetrack $ a  
 $ a and $ a  
 $ A   
 I do not understand why this may not be so. The PHP documentation (and also an example) about this topic can be found there:   
 
 
 This is always  4  is using  post-pay increase  to build the last  $ a   5 , then  Pre-pay Scale  as before  $ a   
  $ a = 1; Resonance ++ $ a + $ a ++; // 4   
 and  
  $ a = 1; Re: ++ $ a + ++ $ a; // 5