XML::Easy::NodeBasics(3pm)

NAME
XML::Easy::NodeBasics - basic manipulation of XML data nodes

SYNOPSIS
    use XML::Easy::NodeBasics qw(xml_content_object xml_element);

    $content = xml_content_object("this", "&", "that");
    $content = xml_content_object(@sublems);

    $element = xml_element("a", { href => "there" }, "there");
    $element = xml_element("div", @subelems);

    use XML::Easy::NodeBasics qw(
        xml_c_content_object xml_c_content_twine);

    $content = xml_c_content_object($content);
    $twine = xml_c_content_twine($content);

    use XML::Easy::NodeBasics qw(
        xml_e_type_name
        xml_e_attributes xml_e_attribute
        xml_e_content_object);

    $type_name = xml_e_type_name($element);
    $attributes = xml_e_attributes($element);
    $href = xml_e_attribute($element, "href");
    $content = xml_e_content_object($element);

    use XML::Easy::NodeBasics qw(
        xml_c_equal xml_e_equal xml_c_unequal xml_e_unequal);

    if(xml_c_equal($content0, $content1)) { ...
    if(xml_e_equal($element0, $element1)) { ...
    if(xml_c_unequal($content0, $content1)) { ...
    if(xml_e_unequal($element0, $element1)) { ...

DESCRIPTION
This module supplies functions concerned with the creation, examination, and other manipulation of XML data nodes (content chunks and elements). The nodes are dumb data objects, best manipulated using plain functions such as the ones in this module.

The nodes are objects of the classes XML::Easy::Content and XML::Easy::Element. The data contained within an existing node cannot be modified. This means that references to nodes can be copied and passed around arbitrarily, without worrying about who might write to them, or deep versus shallow copying. As a result, tasks that you might think of as "modifying an XML node" actually involve creating a new node.

The node classes do not have any interesting object-oriented behaviour, and their minimalistic methods are not meant to be called directly. Instead, node creation and examination should be performed using the functions of this module.

  Twine
For the purposes of examining what is contained within a chunk of content, there is a standard representation of content known as "twine". (It's stronger than a string, and has an alternating structure as will be described.)

A piece of twine is a reference to an array with an odd number of members. The first and last members, and all members in between with an even index, are strings giving the chunk's character data. Each member with an odd index is a reference to an XML::Easy::Element object, representing an XML element contained directly within the chunk. Any of the strings may be empty, if the chunk has no character data between subelements or at the start or end of the chunk.

When not looking inside a content chunk, it is preferred to represent it in encapsulated form as an XML::Easy::Content object.

FUNCTIONS
Each function has two names. There is a longer descriptive name, and a shorter name to spare screen space and the programmer's fingers.

  Construction
The construction functions each accept any number of items of XML content. These items may be supplied in any of several forms. Content item types may be mixed arbitrarily, in any sequence. The permitted forms of content item are:

character data
    A plain string of characters that are acceptable to XML.

element
    A reference to an XML::Easy::Element object representing an XML element.

content object
    A reference to an XML::Easy::Content object representing a chunk of XML content.

twine array
    A reference to a twine array listing a chunk of XML content.

The construction functions are:

xml_content_object(ITEM ...)
xc(ITEM ...)
    Constructs and returns a XML content object based on a list of constituents. Any number of ITEMs (zero or more) may be supplied; each one must be a content item of a permitted type. All the constituents are checked for validity, against the XML 1.0 specification, and the function "die"s if any are invalid.

    All the supplied content items are concatenated to form a single chunk. The function returns a reference to an XML::Easy::Content object.

xml_content_twine(ITEM ...)
xct(ITEM ...)
    Performs the same construction job as "xml_content_object", but returns the resulting content chunk in the form of twine rather than a content object.

    The returned array must not be subsequently modified. If possible, it will be marked as read-only in order to prevent modification.

xml_content(ITEM ...)
    Deprecated alias for "xml_content_twine".

xml_element(TYPE_NAME, ITEM ...)
xe(TYPE_NAME, ITEM ...)
    Constructs and returns an XML::Easy::Element object, representing an XML element, based on a list of consitutents. TYPE_NAME must be a string, and gives the name of the element's type. Any number of ITEMs (zero or more) may be supplied; each one must be either a content item of a permitted type or a reference to a hash of attributes. All the constituents are checked for validity, against the XML 1.0 specification, and the function "die"s if any are invalid.

    All the attributes supplied are gathered together to form the element's attribute set. It is an error if an attribute name has been used more than once (even if the same value was given each time). All the supplied content items are concatenated to form the element's content. The function returns a reference to an XML::Easy::Element object.

  Examination of content chunks

xml_c_content_object(CONTENT)
xc_cont(CONTENT)
    CONTENT must be a reference to either an XML::Easy::Content object or a twine array. Returns a reference to an XML::Easy::Content object encapsulating the content.

xml_c_content_twine(CONTENT)
xc_twine(CONTENT)
    CONTENT must be a reference to either an XML::Easy::Content object or a twine array. Returns a reference to a twine array listing the content.

    The returned array must not be subsequently modified. If possible, it will be marked as read-only in order to prevent modification.

xml_c_content(CONTENT)
    Deprecated alias for "xml_c_content_twine".

  Examination of elements

xml_e_type_name(ELEMENT)
xe_type(ELEMENT)
    ELEMENT must be a reference to an XML::Easy::Element object. Returns the element's type's name, as a string.

xml_e_attributes(ELEMENT)
xe_attrs(ELEMENT)
    ELEMENT must be a reference to an XML::Easy::Element object. Returns a reference to a hash encapsulating the element's attributes. In the hash, each key is an attribute name, and the corresponding value is the attribute's value as a string.

    The returned hash must not be subsequently modified. If possible, it will be marked as read-only in order to prevent modification. As a side effect, the read-only-ness may make lookup of any non-existent attribute generate an exception rather than returning "undef".

xml_e_attribute(ELEMENT, NAME)
xe_attr(ELEMENT, NAME)
    ELEMENT must be a reference to an XML::Easy::Element object. Looks up a specific attribute of the element, by a name supplied as a string. If there is an attribute by that name then its value is returned, as a string. If there is no such attribute then "undef" is returned.

xml_e_content_object(ELEMENT)
xe_cont(ELEMENT)
    ELEMENT must be a reference to an XML::Easy::Element object. Returns a reference to an XML::Easy::Content object encapsulating the element's content.

xml_e_content_twine(ELEMENT)
xe_twine(ELEMENT)
    ELEMENT must be a reference to an XML::Easy::Element object. Returns a reference to a twine array listing the element's content.

    The returned array must not be subsequently modified. If possible, it will be marked as read-only in order to prevent modification.

xml_e_content(ELEMENT)
    Deprecated alias for "xml_e_content_twine".

  Comparison

xml_c_equal(A, B)
xc_eq(A, B)
    A and B must each be a reference to either an XML::Easy::Content object or a twine array. Returns true if they represent exactly the same content, and false if they do not.

xml_e_equal(A, B)
xe_eq(A, B)
    A and B must each be a reference to an XML::Easy::Element object. Returns true if they represent exactly the same element, and false if they do not.

xml_c_unequal(A, B)
xc_ne(A, B)
    A and B must each be a reference to either an XML::Easy::Content object or a twine array. Returns true if they do not represent exactly the same content, and false if they do.

xml_e_unequal(A, B)
xe_ne(A, B)
    A and B must each be a reference to an XML::Easy::Element object. Returns true if they do not represent exactly the same element, and false if they do.

SEE ALSO
XML::Easy::Classify, XML::Easy::Content, XML::Easy::Element, XML::Easy::ProceduralWriter, XML::Easy::SimpleSchemaUtil, XML::Easy::Text

AUTHOR
Andrew Main (Zefram) <zefram@fysh.org>

COPYRIGHT
Copyright (C) 2009, 2010, 2011, 2017 Andrew Main (Zefram) <zefram@fysh.org>

LICENSE
This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.