How to transform structured textfiles into PHP multidimensional array

A way that uses explode to separate each block and a regex to extract the fields:

$pattern = <<<'LOD'
~
# definition
(?<fieldname> (?:HD|BY|WC|PD|SN|SC|PG|LA|CY|LP|TD|CO|IN|NS|RE|IPC|PUB|AN)$ ){0}

# pattern
\G(?<key>\g<fieldname>) \s+
(?<value>
    .+ 
    (?: \R{1,2} (?!\g<fieldname>) .+ )*+
)
(?:\R{1,3}|\z)
~xm
LOD;
$subjects = explode("\r\n\r\n\r\n\r\n", $text);
$result = array();

foreach($subjects as $i => $subject) {
    if (preg_match_all($pattern, $subject, $matches, PREG_SET_ORDER)) {
        foreach ($matches as $match) {
            $result[$i][$match['key']]=$match['value'];
        }
    }
}
echo '<pre>', print_r($result, true);

Pattern details:

The pattern is divided into two parts:

In the definition part I wrote a subpattern named fieldname to use it later in the main pattern. This pattern also checks each fieldname ends a line with the $ anchor.

The main pattern:

\G                        # this forces the match to be contiguous to the
                          # precedent match or the start of the string (no gap)
(?<key> \g<fieldname> )   # a capturing group named "key" for the fieldname
\s+                       # one or more white characters
(?<value>                 # open a capturing group named "value" for the
                          # field content
    .+                    # all characters except newlines 1 or more times
    (?:                   # open an atomic group
        \R\R?+            # one or two newlines to allow paragraphs (LP & TD) 
        (?!\g<fieldname>) # but not followed by a fieldname (only a check)
        .+                #
    )*+                   # close the atomic group and repeat 0 or more times
)                         # close the capture group "value"
(?:\R{1,3}|\z)            # between 1 or 3 newlines max. or the end of the
                          # string (necessary if i want contigous matches)

global modifiers:

• x (Extended mode): whitespaces and inline comments starting with # are ignored in the pattern.
• m (Multiline mode): ^ matches the start of the lines and $ the end of the lines.