Using XML code in PHP scripts with XHP
Rules
A blog post always possesses at least a title, an introduction, and an optional body text. To express such conditions, XHP has the keyword children
(see Listing 10).
Listing 10
Defining Permissible Child Elements
An admin:post
must contain at least one admin:header
and one admin:introduction
. The notation is based on regular expressions.
Table 1 lists all operators that XHP understands. During processing, XHP checks these conditions and aborts if they do not apply. In Listing 10,
<admin:post> <admin:header /> <admin:introduction /> </admin:post>
would be accepted, but the missing introduction,
<admin:post> <admin:header /> </admin:post>
would not.
Table 1
Operators for Children
Symbol | Meaning |
---|---|
|
Zero elements or one element |
|
Zero or multiple elements |
|
One or multiple elements |
|
Or (one of conditions listed to the left and right of | must apply) |
|
The elements listed with a comma must appear in this order |
|
Arbitrary child elements are allowed |
|
No child elements are allowed |
The XHP developers explicitly point out that the underlying "greedy" algorithm takes preference. The children (:elem*, :elem);
condition thus triggers an error: The *
already covers all :elem
; another :elem
thus cannot follow.
If you need to enumerate many elements, you can simplify the task with element categories. In Listing 11, admin:retweet
and admin:tweet
belong to the admin:twittercategory
category. admin:twitter
can have any number of child elements, but they must come from the admin:twittercategory
category.
Listing 11
Use of Element Categories
The x:element
and x:primitive
classes are defined in the code.php
file. The comments stored in these classes also provide the only existing reference documentation. However, the html.php
file contains classes for all HTML elements; for example, :ul
handles the ul
list. Incidentally, the html.php
file also defines the x:doctype
class, which in turn represents the previously mentioned HTML5 document type definition <!DOCTYPE html>
. You currently need to create your own classes for other doctypes, such as XHTML.
The XHP documentation leaves much to be desired. As an introduction, you can read the README.textile
file from the source code archive, which you will also find on GitHub [1]. Additionally, you will find a pretty spartan wiki [3] and the blog posts by Facebook developer Stefan Parker [4]. Among other things, Parker shows how to parameterize CSS code in quite an elegant way using XHP [5].
Conclusions
XHP simplifies programming and input filtering. For example, XHP checks for correct nesting. Unknown elements have no output, and expressions in braces {
… }
are directly processed by htmlspecialchars()
.
Additionally, XHP is quite strict and, for example, takes exception to forgotten or incorrect end tags. Finally, you can quickly create building blocks for a template system using your own elements and tags.
On the other hand, converting the tags into objects costs computing time; in fact, this can be massively expensive depending on the code and usage. According to a comment in the XHP source code, the developers actually expect the APC cache system to be used as an accelerator [6] [7].
Administrators also need to compile, provision, and maintain the extension itself, which is not possible with some web hosting providers. Finally, improved readability depends strongly on the HTML code.
Infos
- XHP: https://github.com/facebook/xhp/tree/master/php-lib
- Documentation on
htmlspecialchars()
: http://php.net/manual/de/function.htmlspecialchars.php - XHP wiki: https://github.com/facebook/xhp/wiki/_pages
- Stefan Parker's blog: http://codebeforethehorse.tumblr.com/
- Stefan Parker: Abstracting CSS with XHP: http://codebeforethehorse.tumblr.com/post/3504948746/abstracting-css-with-xhp
ext.cpp
file: https://github.com/facebook/xhp/blob/master/ext.cpp- APC: http://php.net/manual/en/book.apc.php
« Previous 1 2 3
Buy this article as PDF
(incl. VAT)
Buy Linux Magazine
Subscribe to our Linux Newsletters
Find Linux and Open Source Jobs
Subscribe to our ADMIN Newsletters
Support Our Work
Linux Magazine content is made possible with support from readers like you. Please consider contributing when you’ve found an article to be beneficial.
News
-
Canonical Bumps LTS Support to 12 years
If you're worried that your Ubuntu LTS release won't be supported long enough to last, Canonical has a surprise for you in the form of 12 years of security coverage.
-
Fedora 40 Beta Released Soon
With the official release of Fedora 40 coming in April, it's almost time to download the beta and see what's new.
-
New Pentesting Distribution to Compete with Kali Linux
SnoopGod is now available for your testing needs
-
Juno Computers Launches Another Linux Laptop
If you're looking for a powerhouse laptop that runs Ubuntu, the Juno Computers Neptune 17 v6 should be on your radar.
-
ZorinOS 17.1 Released, Includes Improved Windows App Support
If you need or desire to run Windows applications on Linux, there's one distribution intent on making that easier for you and its new release further improves that feature.
-
Linux Market Share Surpasses 4% for the First Time
Look out Windows and macOS, Linux is on the rise and has even topped ChromeOS to become the fourth most widely used OS around the globe.
-
KDE’s Plasma 6 Officially Available
KDE’s Plasma 6.0 "Megarelease" has happened, and it's brimming with new features, polish, and performance.
-
Latest Version of Tails Unleashed
Tails 6.0 is based on Debian 12 and includes GNOME 43.
-
KDE Announces New Slimbook V with Plenty of Power and KDE’s Plasma 6
If you're a fan of KDE Plasma, you'll be thrilled to hear they've announced a new Slimbook with an AMD CPU and the latest version of KDE Plasma desktop.
-
Monthly Sponsorship Includes Early Access to elementary OS 8
If you want to get a glimpse of what's in the pipeline for elementary OS 8, just set up a monthly sponsorship to help fund its continued existence.