NOTES:

Note 1) PXML_schema.xsd is overly picky about line-ordering; the line order is not required in practice,
        but requiring the ordering makes the validator happy; this the validator may reject a valid PXML.xml
Note 2) libpnd is not (currently) as picky as the validator (since it only consumes some values, and will
        sometimes 'trust' bad values in hopes things will just work anyway), but many of the online download
        repositories _will_ use this validator, so it is probably a good idea to make your PXMLs conform!
Note 3) These points aside -- anything passing the validator should pass into libpnd just fint; PXML.xmls that
        do not pass the validator may well work with libpnd, depending on the nature of the rejection --
        if the PXML.xml is just bad, fix it! But if the validator rejects the PXML.xml on grounds of
        bad categories or line ordering or whatever, then libpnd will 'accept' the application, but may
        massage things to work.
Note 4) minimenu and xfce and other Freedesktop Statandard adhering applications may actually be pickier about
        some things than the validator -- the validator will verify the categories and subcategories are
        known to the Freedesktop spec, but does not validate that a FD subcategory actually belongs to the
        listed parent category. 

Now, onto the actual specification:

1) at the root there is *exactly* one PXML block
2) inside this PXML block are >=1 <application> blocks
        (required) id=DUMBFOLDERNAME
        (optional) appdata=DUMBFOLDERNAME

inside each application block:
1) =1 <exec>
        (required) command=TOKEN
        (optional) arguments=TOKEN
        (optional) background=BOOLEAN
        (optional) startdir=DUMBPATH
        (optional) standalone=BOOLEAN
        (optional) x11=[req|stop|ignore]
2) >=1 <title>TEXT</title>
        (required) lang=LANGCODE ( [a-zA-Z]{2,3}(_[a-zA-Z0-9]{2,3})* )
3) =1 <author>
        (required) name=TEXT
        (optional) website=anyURI
        (optional) email=EMAILADDRESS
4) =1 <version>
        (required) major=VERSION_NR
        (required) minor=VERSION_NR
        (required) release=VERSION_NR
        (required) build=VERSION_NR
5) <=1 <osversion>
        (required) major=VERSION_NR
        (required) minor=VERSION_NR
        (required) release=VERSION_NR
        (required) build=VERSION_NR
6) >=0 <description>TEXT</description>
        (required) lang=LANGCODE ( [a-zA-Z]{2,3}(_[a-zA-Z0-9]{2,3})* )
7) <=1 <icon>
        (required) src=DUMBPATH
8) <=1 <previewpics>
        (optional) >=0 <pic>
                        (required) src=DUMBPATH
9) <=1 <info>
        (required) name=TEXT
        (required) type=[text/html|text/plain]
        (required) src=DUMBPATH
10)=1 <categories>
        (required) >=1 <category>
                        (required) name=fdoCategory
                        (optional) <subcategory>
                                  (required) name=fdoSubCategory
11)<=1 <associations>
        (required) >=1 <association>
                        (required) name=TEXT
                        (required) filetype=TOKEN
                        (required) arguments=TOKEN
12)<=1 <clockspeed>
        (required) frequency=positiveInteger



Filetype/variable explaination:
anyURI: should be some URL, no idea what exactly XML accepts there... (XML variable 'anyURI'!)
BOOLEAN: 0 or 1 or true or false (XML variable 'boolean'!)
DUMBFOLDERNAME: TEXT without ?>:/
DUMBPATH: TEXT without ?>:
EMAILADDRESS: [^@]+@[^\.]+\..+      in normal lang: something with an @ in the middle and some domain like thingie
LANGCODE: [a-zA-Z]{2,3}(_[a-zA-Z0-9]{2,3})*   example: en, eng, en_US, fur_IT
TEXT: The normalizedString data type also contains characters, but the XML processor will remove line feeds, carriage returns, and tab characters. (XML variable 'normalizedString'!)
TOKEN: The token data type also contains characters, but the XML processor will remove line feeds, carriage returns, tabs, leading and trailing spaces, and multiple spaces. (XML variable 'token'!)
VERSION_NR: [a-zA-Z0-9+-]*   example: 1, a, +svn, -svn, 123456789123456789

fdoCategory=AudioVideo|Audio|Video|Development|Education|Game|Graphics|Network|Office
fdoSubCategory=Building|Debugger|IDE|GUIDesigner|Profiling|RevisionControl|Translation|Calendar|ContactManagement|Database|Dictionary|Chart|Email|Finance|FlowChart|PDA|ProjectManagement|Presentation|Spreadsheet|WordProcessor|2DGraphics|VectorGraphics|RasterGraphics|3DGraphics|Scanning|OCR|Photography|Publishing|Viewer|TextTools|DesktopSettings|HardwareSettings|Printing|PackageManager|Dialup|InstantMessaging|Chat|IRCClient|FileTransfer|HamRadio|News|P2P|RemoteAccess|Telephony|TelephonyTools|VideoConference|WebBrowser|WebDevelopment|Midi|Mixer|Sequencer|Tuner|TV|AudioVideoEditing|Player|Recorder|DiscBurning|ActionGame|AdventureGame|ArcadeGame|BoardGame|BlocksGame|CardGame|KidsGame|LogicGame|RolePlaying|Simulation|SportsGame|StrategyGame|Art|Construction|Music|Languages|Science|ArtificialIntelligence|Astronomy|Biology|Chemistry|ComputerScience|DataVisualization|Economy|Electricity|Geography|Geology|Geoscience|History|ImageProcessing|Literature|Math|NumericalAnalysis|MedicalSoftware|Physics|Robotics|Sports|ParallelComputing|Amusement|Archiving|Compression|Electronics|Emulator|Engineering|FileTools|FileManager|TerminalEmulator|Filesystem|Monitor|Security|Accessibility|Calculator|Clock|TextEditor|Documentation|Core|KDE|GNOME|GTK|Qt|Motif|Java|ConsoleOnly