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>.