<?php
 
$string = "Lot99. Is it 1+3 or 5 or 6.53";
$regex = '~
            (?:\d+\.\d+)    # looks for digits with a point (float)
            (*SKIP)(*FAIL)  # all of the left alternatives should fail
            |               # OR
            ([.\s+]+)       # a point, whitespace or plus sign 
                            # this should match and be captured
                            # for PREG_SPLIT_DELIM_CAPTURE
          ~x';              # verbose modifier
$parts = preg_split($regex, $string, 0, PREG_SPLIT_DELIM_CAPTURE);
print_r($parts);
?>

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