Why elseif instead of else if?

Question

Few days ago I stopped on some PHP's developers quide (for contributors to particular project) and it stated, that elseif must be strictly used instead of else if -- without giving any reason, why?

Can someone clarify this? I don't see neither much difference nor any argument supporting this.

Info: I believe, there are more languages, than just PHP, that this problem strikes, that's why I asked here, not on Stack Overflow. Feel free to migrate, if necessary.

Answer 1

The behavior when using curly brackets is exactly the same. However when not using curly brackets but colon instead, the following will not compile:

if($a > $b):
    echo $a." is greater than ".$b;
else if($a == $b): // Will not compile.
    echo "The above line causes a parse error.";
endif;

I assume that the reason for preferring elseif over else if is either to be able to switch to and from curly brackets without creating a compile error or, probably more likely, it is a stylistic choice and prefers that only elseif is used.

According to the php documentation:

Nota: Note that elseif and else if will only be considered exactly the same when using curly brackets as in the above example. When using a colon to define your if/elseif conditions, you must not separate else if into two words, or PHP will fail with a parse error.

Answer 2

Besides this answer, in both PSR2.0 and PEAR coding standards the use of elseif instead of else if is specified so that all control keywords look like single words:

<?php 
if ($expr1) {
    // if body 
} elseif ($expr2) {
    // elseif body 
} else {
    // else body; 
}

The keyword elseif SHOULD be used instead of else if so that all control keywords look like single words

Source: https://github.com/php-fig/fig-standards/blob/master/accepted/PSR-2-coding-style-guide.md#51-if-elseif-else