replace all line breaks between specific BBCode tags

I'm programming a wiki with BBCode-like editing syntax.
I want the user to be allowed to enter line breaks that resolve to <br> tags.
Until here there's no problem occuring.

Now i also have the following lines, that should convert into a table:

[table]
    [row]
        [col]Column1[/col]
        [col]Column2[/col]
        [col]Column3[/col]
    [/row]
[/table]

All those line breaks, that were entered when formatting the editable BBCode above are creating <br> tags that are forced to be rendered in front of the html-table.

My goal is to remove all line breaks between [table] and [/table] in my parser function using php's preg_replace without breaking the possibility to enter normal text using newlines.

This is my parsing function so far:

function richtext($text)
{
    $text = htmlspecialchars($text);

    $expressions = array(
        # Poor attempts
        '/[table](rn*)|(r*)|(n*)[/table]/' => '',
        '/[table]([^n]*?n+?)+?[/table]/' => '',
        '/[table].*?(r+).*?[/table]/' => '',
        # Line breaks
        '/rn|r|n/' => '<br>'
    );

    foreach ($expressions as $pattern => $replacement)
    {
        $text = preg_replace($pattern, $replacement, $text);
    }

    return $text;
}

It would be great if you could also explain a bit what the regex is doing.

---

Style

First of all, you don't need the foreach loop, preg_replace accepts mixed variables, eg arrays, see Example #2: http://www.php.net/manual/en/function.preg-replace.php

Answer

Use this regex to remove all line breaks between two tags (here table and row):

([table]([^rn]*))(rn)*([^rn]*[row])

The tricky part is to replace it (See also this: preg_replace() Only Specific Part Of String):

$result = preg_replace('/([table][^rn]*)(rn)*([^rn]*[row])/', '$1$4', $subject);

Instead of replacing with '' , you replace it only the second group ( (rn)* ) with '$1$4' .

Example

[table] // This will also work with multiple line breaks
    [row]
        [col]Column1[/col]
        [col]Column2[/col]
        [col]Column3[/col]
    [/row]
[/table]

With the regex, this will output:

[table]    [row]
        [col]Column1[/col]
        [col]Column2[/col]
        [col]Column3[/col]
    [/row]
[/table] 

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