[pmwiki-users] relative position style

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On Fri, May 10, 2013 at 4:31 PM, Mark Lee <mark.lee.phd at gmail.com> wrote:
> Peter,
> 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.
> Specifically:
>      1. If the page is in the Plant group, and the (:plant ... :) markup is
> used on the page, then include the garden map.

Could you do something like this:

(:if group "Plant":)(:plant ...:)(:if)

?

>      2. If I don't use the (:plant ... :) markup, the garden map is not
> included.

This would be the default case, would it not?

> Is this possible?
>
> -Mark
>
>
> 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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