[pmwiki-users] relative position style

Mark Lee mark.lee.phd at gmail.com
Fri May 10 16:31:17 CDT 2013

I am having success with your method. I have a map of the garden, and I can
place a single red "X" on the map using the markup
  (:plant x=100 y=200:);
I used your code (mostly unchanged) in my config.php file. Thank you again!

The next thing I want to do is add this feature to my skin. I have already
played around with my skin.tmpl file, but I am not sure how to do this
conditional markup.
     1. If the page is in the Plant group, and the (:plant ... :) markup is
used on the page, then include the garden map.
     2. If I don't use the (:plant ... :) markup, the garden map is not
Is this possible?


On Thu, May 9, 2013 at 12:38 AM, Peter Bowers <pbowers at pobox.com> wrote:

> On Thu, May 9, 2013 at 2:26 AM, Mark Lee <mark.lee.phd at gmail.com> wrote:
>> Thanks Peter. So helpful.
>> I have been reading about regular expressions. I am wondering why we need
>> "\\" in the pattern  '/\\(:plant\\s*(.*?):\\)/e'? I know that "\(" means
>> the "(" character, but what does "\\(" mean? The extra "\" is also used
>> before "\s" and "\)". Is that part of pmwiki?
>> No, none of that has anything specific to do with pmwiki -- it's how PHP
> string handling and regex handling functions.
> The following characters are "magic" in regular expressions:
> (, ), \s, \d, *, ., etc.
> By "magic" I mean they do not match themselves.  If in your regular
> expression you have an "a" it will match exactly that -- another "a".  But
> if you have one of those "magic" characters then they have another meaning
> -- a '(' will not match a '(' in your regular expression (it tells the
> regex engine to start a pattern grouping) and the 2 characters '\s' will
> not match the 2 characters '\s' (they tell the regex engine to match any
> whitespace - space, enter, tab, etc.).
> But what do you do if you want to match one of these "magic" characters?
> In this case you want to match an open-paren and a close-paren so you can
> match the first and last characters of "(:plant ...:)".
> In order to "unmagic" a "magic" character you escape it -- which means you
> put a backslash in front of it.
> Thus '\(' matches '(' and '\)' matches ')' and '\\s' matches '\s' and
> etc.  In each case the backslash removes the specialness of the character
> that follows.  (Note that in the case of the '\\s' you are actually
> "unmagic'ing" the backslash -- once the s doesn't have a backslash in front
> of it then it is just a normal character.)
> Now, if that wasn't complicated enough ... we also have to work with the
> special rules of quoting strings in PHP.  And it truly gets complicated
> here between single quotes and double quotes (the rules are very different
> depending on which one you are using).
> PHP uses the same idea of "escaping" to remove any special meaning of a
> character within quotes.  So if you wanted to put the string **I don't
> care** in single quotes without escaping it would look like this: 'I don't
> care'.  Obviously this causes a problem because PHP sees the apostrophe
> between don and t and identifies it as the end of the string and the
> following **t care'** is simply a syntactical error.  So what you do is you
> escape the single quote with a backslash: 'I don\'t care'.  The backslash
> removes the special meaning of the single-quote as an
> end-of-string-delimiter and results in a valid string delimited by single
> quotes and containing a single quote.  The important thing to note is that
> the string NO LONGER CONTAINS THE BACKSLASH.  PHP removes the escaping
> backslashes as soon as they have done their job.  And even if from PHP's
> perspective they have no job (s has no special meaning within a PHP string
> so the backslash before \s doesn't really have a function) they still
> remove those backslashes.
> But in order to have your regex contain a backslash you have to somehow
> make PHP allow the backslash through.  You do that by, you guessed it,
> escaping it with another backslash.  So a double-backslash (\\) in a PHP
> string will be converted to a single-backslash (\) by PHP string handling.
> So, back to the original example: '/\\(:plant\\s*(.*?):\\)/e'
> After PHP string handling finishes with it it will be stored internally
> like this: '/\(:plant\s*(.*?):\)/e' (I've just removed one of each of the
> pairs of backslashes.)
> NOW it is clear that the regex engine can look at \( and see it as
> matching a literal ( and it can see the \s and see it as matching any
> whitespace and etc.
> Sometimes the eval that is implicit in the /.../e requires more escaping
> and it gets really confusing -- you just have to think that each "pass"
> which allows escaping is going to remove one of any pair of backslashes.
> So you count how many passes (first PHP string handling, then the regex
> engine, then the eval call -- and there can be others in there as well).
> Eventually after you've pulled out all your hair you just start adding
> backslashes one at a time until it finally does what you want.
> How's that for a much longer and more in-depth explanation than you really
> wanted? :-)
> -Peter
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