NAME

       XML::Filter::DetectWS - A PerlSAX filter that detects ignorable whitespace

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 ignorable 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 surrounding 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

       •   SkipIgnorableWS (Default: 0)

           When set, detected ignorable whitespace is discarded.

       •   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:

       •   1 (WS_START) - whitespace immediately after element-start tag

       •   2 (WS_END) - whitespace just before element-end tag

       •   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

       •   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 processing 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 positions may need some work.

AUTHOR

       Enno Derksen is the Original Author.

       Send bug reports, hints, tips, suggestions to T.J. Mather at <tjmather@tjmather.com>.