This function returns a string or an array with all occurrences of
   search in subject
   (ignoring case) replaced with the given replace
   value.  If you don't need fancy replacing rules, you should generally
   use this function instead of
   preg_replace() with the i modifier.
  
   If search and replace are
   arrays, then str_ireplace() takes a value from each
   array and uses them to search and replace on
   subject. If replace has fewer
   values than search, then an empty string is used for
   the rest of replacement values. If search is an
   array and replace is a string, then this replacement
   string is used for every value of search. The
   converse would not make sense, though.
  
   If search or replace
   are arrays, their elements are processed first to last.
  
searchThe value being searched for, otherwise known as the needle. An array may be used to designate multiple needles.
replace
       The replacement value that replaces found search
       values. An array may be used to designate multiple replacements.
      
subjectThe string or array being searched and replaced on, otherwise known as the haystack.
       If subject is an array, then the search and
       replace is performed with every entry of 
       subject, and the return value is an array as
       well.
      
countIf passed, this will be set to the number of replacements performed.
Returns a string or an array of replacements.
Example #1 str_ireplace() example
<?php
$bodytag = str_ireplace("%body%", "black", "<body text=%BODY%>");
?>
Note: This function is binary-safe.
Because str_ireplace() replaces left to right, it might replace a previously inserted value when doing multiple replacements. Example #2 in the str_replace() documentation demonstrates how this may affect you in practice.