{source}<?php $a= "{article}[field1:value]{/article}";
$b= "{article}[field2:value]{/article}";
$c = $a + $b;
echo $c;
?>{/source}
{source}<?php $a= (int) "{article}[field1:value]{/article}";
$b= (int) "{article}[field2:value]{/article}";
$c = $a + $b;
echo $c;
?>{/source}
{source}<?php
$a = "{article}[field1:value]{/article}XXX";
echo $a[0];
?>{/source}
{article}{source}<?php $a= "[field1:value]";
$b= "[field2:value]";
$c = $a + $b;
echo $c;
?>{/source}{/article}