XML::Filter::DetectWS

XML::Filter::DetectWS(User Contributed Perl DocumentatXML::Filter::DetectWS(3)



NAME
       XML::Filter::DetectWS - A PerlSAX filter that detects ignorable whites-
       pace

SYNOPSIS
        use XML::Filter::DetectWS;

        my $detect = new XML::Filter::DetectWS (Handler => $handler,
                                                SkipIgnorableWS => 1);

DESCRIPTION
       This a PerlSAX filter that detects which character data contains ignor-
       able whitespace and optionally filters it.

       Note that this is just a first stab at the implementation and it may
       change completely in the near future. Please provide feedback whether
       you like it or not, so I know whether I should change it.

       The XML spec defines ignorable whitespace as the character data found
       in elements that were defined in an <!ELEMENT> declaration with a model
       of 'EMPTY' or 'Children' (Children is the rule that does not contain
       '#PCDATA'.)

       In addition, XML::Filter::DetectWS allows the user to define other
       whitespace to be ignorable. The ignorable whitespace is passed to the
       PerlSAX Handler with the ignorable_whitespace handler, provided that
       the Handler implements this method. (Otherwise it is passed to the
       characters handler.)  If the SkipIgnorableWS is set, the ignorable
       whitespace is simply discarded.

       XML::Filter::DetectWS also takes xml:space attributes into account. See
       below for details.

       CDATA sections are passed in the standard PerlSAX way (i.e. with sur-
       rounding start_cdata and end_cdata events), unless the Handler does not
       implement these methods. In that case, the CDATA section is simply
       passed to the characters method.

Constructor Options
       o SkipIgnorableWS (Default: 0)
           When set, detected ignorable whitespace is discarded.

       o Handler
           The PerlSAX handler (or filter) that will receive the PerlSAX
           events from this filter.

Current Implementation
       When determining which whitespace is ignorable, it first looks at the
       xml:space attribute of the parent element node (and its ancestors.)  If
       the attribute value is "preserve", then it is *NOT* ignorable.  (If
       someone took the trouble of adding xml:space="preserve", then that is
       the final answer...)

       If xml:space="default", then we look at the <!ELEMENT> definition of
       the parent element. If the model is 'EMPTY' or follows the 'Children'
       rule (i.e. does not contain '#PCDATA') then we know that the whitespace
       is ignorable.  Otherwise we need input from the user somehow.

       The idea is that the API of DetectWS will be extended, so that you can
       specify/override e.g. which elements should behave as if
       xml:space="preserve" were set, and/or which elements should behave as
       if the <!ELEMENT> model was defined a certain way, etc.

       Please send feedback!

       The current implementation also detects whitespace after an element-
       start tag, whitespace before an element-end tag.  It also detects
       whitespace before an element-start and after an element-end tag and
       before or after comments, processing instruction, cdata sections etc.,
       but this needs to be reimplemented.  In either case, the detected
       whitespace is split off into its own PerlSAX characters event and an
       extra property 'Loc' is added. It can have 4 possible values:

       o 1 (WS_START) - whitespace immediately after element-start tag
       o 2 (WS_END) - whitespace just before element-end tag
       o 3 (WS_ONLY) - both WS_START and WS_END, i.e. it's the only text found
       between the start and end tag and it's all whitespace
       o 0 (WS_INTER) - none of the above, probably before an element-start
       tag, after an element-end tag, or before or after a comment, PI, cdata
       section etc.

       Note that WS_INTER may not be that useful, so this may change.

xml:space attribute
       The XML spec states that: A special attribute named xml:space may be
       attached to an element to signal an intention that in that element,
       white space should be preserved by applications.  In valid documents,
       this attribute, like any other, must be declared if it is used.  When
       declared, it must be given as an enumerated type whose only possible
       values are "default" and "preserve".  For example:

        <!ATTLIST poem   xml:space (default|preserve) 'preserve'>

       The value "default" signals that applications' default white-space pro-
       cessing modes are acceptable for this element; the value "preserve"
       indicates the intent that applications preserve all the white space.
       This declared intent is considered to apply to all elements within the
       content of the element where it is specified, unless overriden with
       another instance of the xml:space attribute.

       The root element of any document is considered to have signaled no
       intentions as regards application space handling, unless it provides a
       value for this attribute or the attribute is declared with a default
       value.

       [... end of excerpt ...]

CAVEATS
       This code is highly experimental!  It has not been tested well and the
       API may change.

       The code that detects of blocks of whitespace at potential indent posi-
       tions may need some work. See

AUTHOR
       Send bug reports, hints, tips, suggestions to Enno Derksen at
       <enno@att.com>.



perl v5.8.0                       2000-02-17          XML::Filter::DetectWS(3)