sgml_write.pl -- XML/SGML writer module

This library provides the inverse functionality of the sgml.pl parser library, writing XML, SGML and HTML documents from the parsed output. It is intended to allow rewriting in a different dialect or encoding or to perform document transformation in Prolog on the parsed representation.

The current implementation is particularly keen on getting character encoding and the use of character entities right. Some work has been done providing layout, but space handling in XML and SGML make this a very hazardous area.

The Prolog-based low-level character and escape handling is the real bottleneck in this library and will probably be moved to C in a later stage.

See also

- library(http/html_write) provides a high-level library for emitting HTML and XHTML.

 xml_write(+Data, +Options) is det

 sgml_write(+Data, +Options) is det

 html_write(+Data, +Options) is det

 xml_write(+Stream, +Data, +Options) is det

 sgml_write(+Stream, +Data, +Options) is det

 html_write(+Stream, +Data, +Options) is det

Write a term as created by the SGML/XML parser to a stream in SGML or XML format. Options:

cleanns(Bool)

If true (default), remove duplicate xmlns attributes.

dtd(DTD)

The DTD. This is needed for SGML documents that contain elements with content model EMPTY. Characters which may not be written directly in the Stream's encoding will be written using character data entities from the DTD if at all possible, otherwise as numeric character references. Note that the DTD will NOT be written out at all; as yet there is no way to write out an internal subset, though it would not be hard to add one.

doctype(DocType)

Document type for the SGML document type declaration. If omitted it is taken from the root element. There is never any point in having this be disagree with the root element. A <!DOCTYPE> declaration will be written if and only if at least one of doctype(_), public(_), or system(_) is provided in Options.

public PubId

The public identifier to be written in the <!DOCTYPE> line.

system(SysId)

The system identifier to be written in the <!DOCTYPE> line.

header(Bool)

If Bool is 'false', do not emit the <xml ...> header line. (xml_write/3 only)

nsmap(Map:list(Id=URI))

When emitting embedded XML, assume these namespaces are already defined from the environment. (xml_write/3 only).

indent(Indent)

Indentation of the document (for embedding)

layout(Bool)

Emit/do not emit layout characters to make output readable.

net(Bool)

Use/do not use Null End Tags. For XML, this applies only to empty elements, so you get

    <foo/>      (default, net(true))
    <foo></foo> (net(false))

For SGML, this applies to empty elements, so you get

    <foo>       (if foo is declared to be EMPTY in the DTD)
    <foo></foo> (default, net(false))
    <foo//      (net(true))

and also to elements with character content not containing /

    <b>xxx</b>  (default, net(false))
    <b/xxx/     (net(true)).

Note that if the stream is UTF-8, the system will write special characters as UTF-8 sequences, while if it is ISO Latin-1 it will use (character) entities if there is a DTD that provides them, otherwise it will use numeric character references.

 emit_doctype(+Options, +Data, +Stream)[private]

Emit the document-type declaration. There is a problem with the first clause if we are emitting SGML: the SGML DTDs for HTML up to HTML 4 do not allow any 'version' attribute; so the only time this is useful is when it is illegal!

 emit(+Element, +Out, +State, +Options)[private]

Emit a single element

 update_nsmap(+Attributes, -Attributes1, !State)[private]

Modify the nsmap of State to reflect modifications due to xmlns arguments.

Arguments:

Attributes1

- is a copy of Attributes with all redundant namespace attributes deleted.

 content(+Content, +Out, +Element, +State, +Options)[private]

Emit the content part of a structure as well as the termination for the content. For empty content we have three versions: XML style '/>', SGML declared EMPTY element (nothing) or normal SGML element (we must close with the same element name).

 add_missing_namespaces(+DOM0, +NsMap, -DOM)[private]

Add xmlns:NS=URI definitions to the toplevel element(s) to deal with missing namespaces.

 generate_ns(+URI, -NS, -URL) is det[private]

Generate a namespace (NS) identifier for URI.

 xmlns(?NS, ?URI) is nondet[multifile]

Hook to define human readable abbreviations for XML namespaces. xml_write/3 tries these locations:

1. This hook
2. Defaults (see below)
3. rdf_db:ns/2 for RDF-DB integration

Default XML namespaces are:

xsi	http://www.w3.org/2001/XMLSchema-instance
xs	http://www.w3.org/2001/XMLSchema
xhtml	http://www.w3.org/1999/xhtml
soap11	http://schemas.xmlsoap.org/soap/envelope/
soap12	http://www.w3.org/2003/05/soap-envelope

See also

- xml_write/2, rdf_register_ns/2.

 missing_namespaces(+DOM, +NSMap, -Missing)[private]

Return a list of URIs appearing in DOM that are not covered by xmlns definitions.

 writeq(+Text:codes, +Out:stream, +Escape:atom, +Escape:assoc) is det[private]

 empty_element(+State, +Element)[private]

True if Element is declared with EMPTY content in the (SGML) DTD.

 dtd_character_entities(+DTD, -Map)[private]

Return an assoc mapping character entities to their name. Note that the entity representation is a bit dubious. Entities should allow for a wide-character version and avoid the &#..; trick.

Re-exported predicates

The following predicates are exported from this file while their implementation is defined in imported modules or non-module files loaded by this module.

 xml_write(+Data, +Options) is det

 sgml_write(+Data, +Options) is det

 html_write(+Data, +Options) is det

 xml_write(+Stream, +Data, +Options) is det

 sgml_write(+Stream, +Data, +Options) is det

 html_write(+Stream, +Data, +Options) is det

Write a term as created by the SGML/XML parser to a stream in SGML or XML format. Options:

cleanns(Bool)

If true (default), remove duplicate xmlns attributes.

dtd(DTD)

The DTD. This is needed for SGML documents that contain elements with content model EMPTY. Characters which may not be written directly in the Stream's encoding will be written using character data entities from the DTD if at all possible, otherwise as numeric character references. Note that the DTD will NOT be written out at all; as yet there is no way to write out an internal subset, though it would not be hard to add one.

doctype(DocType)

Document type for the SGML document type declaration. If omitted it is taken from the root element. There is never any point in having this be disagree with the root element. A <!DOCTYPE> declaration will be written if and only if at least one of doctype(_), public(_), or system(_) is provided in Options.

public PubId

The public identifier to be written in the <!DOCTYPE> line.

system(SysId)

The system identifier to be written in the <!DOCTYPE> line.

header(Bool)

If Bool is 'false', do not emit the <xml ...> header line. (xml_write/3 only)

nsmap(Map:list(Id=URI))

When emitting embedded XML, assume these namespaces are already defined from the environment. (xml_write/3 only).

indent(Indent)

Indentation of the document (for embedding)

layout(Bool)

Emit/do not emit layout characters to make output readable.

net(Bool)

Use/do not use Null End Tags. For XML, this applies only to empty elements, so you get

    <foo/>      (default, net(true))
    <foo></foo> (net(false))

For SGML, this applies to empty elements, so you get

    <foo>       (if foo is declared to be EMPTY in the DTD)
    <foo></foo> (default, net(false))
    <foo//      (net(true))

and also to elements with character content not containing /

    <b>xxx</b>  (default, net(false))
    <b/xxx/     (net(true)).

Note that if the stream is UTF-8, the system will write special characters as UTF-8 sequences, while if it is ISO Latin-1 it will use (character) entities if there is a DTD that provides them, otherwise it will use numeric character references.

 xml_write(+Data, +Options) is det

 sgml_write(+Data, +Options) is det

 html_write(+Data, +Options) is det

 xml_write(+Stream, +Data, +Options) is det

 sgml_write(+Stream, +Data, +Options) is det

 html_write(+Stream, +Data, +Options) is det

Write a term as created by the SGML/XML parser to a stream in SGML or XML format. Options:

cleanns(Bool)

If true (default), remove duplicate xmlns attributes.

dtd(DTD)

The DTD. This is needed for SGML documents that contain elements with content model EMPTY. Characters which may not be written directly in the Stream's encoding will be written using character data entities from the DTD if at all possible, otherwise as numeric character references. Note that the DTD will NOT be written out at all; as yet there is no way to write out an internal subset, though it would not be hard to add one.

doctype(DocType)

Document type for the SGML document type declaration. If omitted it is taken from the root element. There is never any point in having this be disagree with the root element. A <!DOCTYPE> declaration will be written if and only if at least one of doctype(_), public(_), or system(_) is provided in Options.

public PubId

The public identifier to be written in the <!DOCTYPE> line.

system(SysId)

The system identifier to be written in the <!DOCTYPE> line.

header(Bool)

If Bool is 'false', do not emit the <xml ...> header line. (xml_write/3 only)

nsmap(Map:list(Id=URI))

When emitting embedded XML, assume these namespaces are already defined from the environment. (xml_write/3 only).

indent(Indent)

Indentation of the document (for embedding)

layout(Bool)

Emit/do not emit layout characters to make output readable.

net(Bool)

Use/do not use Null End Tags. For XML, this applies only to empty elements, so you get

    <foo/>      (default, net(true))
    <foo></foo> (net(false))

For SGML, this applies to empty elements, so you get

    <foo>       (if foo is declared to be EMPTY in the DTD)
    <foo></foo> (default, net(false))
    <foo//      (net(true))

and also to elements with character content not containing /

    <b>xxx</b>  (default, net(false))
    <b/xxx/     (net(true)).

Note that if the stream is UTF-8, the system will write special characters as UTF-8 sequences, while if it is ISO Latin-1 it will use (character) entities if there is a DTD that provides them, otherwise it will use numeric character references.

 xml_write(+Data, +Options) is det

 sgml_write(+Data, +Options) is det

 html_write(+Data, +Options) is det

 xml_write(+Stream, +Data, +Options) is det

 sgml_write(+Stream, +Data, +Options) is det

 html_write(+Stream, +Data, +Options) is det

Write a term as created by the SGML/XML parser to a stream in SGML or XML format. Options:

cleanns(Bool)

If true (default), remove duplicate xmlns attributes.

dtd(DTD)

The DTD. This is needed for SGML documents that contain elements with content model EMPTY. Characters which may not be written directly in the Stream's encoding will be written using character data entities from the DTD if at all possible, otherwise as numeric character references. Note that the DTD will NOT be written out at all; as yet there is no way to write out an internal subset, though it would not be hard to add one.

doctype(DocType)

Document type for the SGML document type declaration. If omitted it is taken from the root element. There is never any point in having this be disagree with the root element. A <!DOCTYPE> declaration will be written if and only if at least one of doctype(_), public(_), or system(_) is provided in Options.

public PubId

The public identifier to be written in the <!DOCTYPE> line.

system(SysId)

The system identifier to be written in the <!DOCTYPE> line.

header(Bool)

If Bool is 'false', do not emit the <xml ...> header line. (xml_write/3 only)

nsmap(Map:list(Id=URI))

When emitting embedded XML, assume these namespaces are already defined from the environment. (xml_write/3 only).

indent(Indent)

Indentation of the document (for embedding)

layout(Bool)

Emit/do not emit layout characters to make output readable.

net(Bool)

Use/do not use Null End Tags. For XML, this applies only to empty elements, so you get

    <foo/>      (default, net(true))
    <foo></foo> (net(false))

For SGML, this applies to empty elements, so you get

    <foo>       (if foo is declared to be EMPTY in the DTD)
    <foo></foo> (default, net(false))
    <foo//      (net(true))

and also to elements with character content not containing /

    <b>xxx</b>  (default, net(false))
    <b/xxx/     (net(true)).

Note that if the stream is UTF-8, the system will write special characters as UTF-8 sequences, while if it is ISO Latin-1 it will use (character) entities if there is a DTD that provides them, otherwise it will use numeric character references.

 xml_write(+Data, +Options) is det

 sgml_write(+Data, +Options) is det

 html_write(+Data, +Options) is det

 xml_write(+Stream, +Data, +Options) is det

 sgml_write(+Stream, +Data, +Options) is det

 html_write(+Stream, +Data, +Options) is det

Write a term as created by the SGML/XML parser to a stream in SGML or XML format. Options:

cleanns(Bool)

If true (default), remove duplicate xmlns attributes.

dtd(DTD)

The DTD. This is needed for SGML documents that contain elements with content model EMPTY. Characters which may not be written directly in the Stream's encoding will be written using character data entities from the DTD if at all possible, otherwise as numeric character references. Note that the DTD will NOT be written out at all; as yet there is no way to write out an internal subset, though it would not be hard to add one.

doctype(DocType)

Document type for the SGML document type declaration. If omitted it is taken from the root element. There is never any point in having this be disagree with the root element. A <!DOCTYPE> declaration will be written if and only if at least one of doctype(_), public(_), or system(_) is provided in Options.

public PubId

The public identifier to be written in the <!DOCTYPE> line.

system(SysId)

The system identifier to be written in the <!DOCTYPE> line.

header(Bool)

If Bool is 'false', do not emit the <xml ...> header line. (xml_write/3 only)

nsmap(Map:list(Id=URI))

When emitting embedded XML, assume these namespaces are already defined from the environment. (xml_write/3 only).

indent(Indent)

Indentation of the document (for embedding)

layout(Bool)

Emit/do not emit layout characters to make output readable.

net(Bool)

Use/do not use Null End Tags. For XML, this applies only to empty elements, so you get

    <foo/>      (default, net(true))
    <foo></foo> (net(false))

For SGML, this applies to empty elements, so you get

    <foo>       (if foo is declared to be EMPTY in the DTD)
    <foo></foo> (default, net(false))
    <foo//      (net(true))

and also to elements with character content not containing /

    <b>xxx</b>  (default, net(false))
    <b/xxx/     (net(true)).

Note that if the stream is UTF-8, the system will write special characters as UTF-8 sequences, while if it is ISO Latin-1 it will use (character) entities if there is a DTD that provides them, otherwise it will use numeric character references.

 xml_write(+Data, +Options) is det

 sgml_write(+Data, +Options) is det

 html_write(+Data, +Options) is det

 xml_write(+Stream, +Data, +Options) is det

 sgml_write(+Stream, +Data, +Options) is det

 html_write(+Stream, +Data, +Options) is det

Write a term as created by the SGML/XML parser to a stream in SGML or XML format. Options:

cleanns(Bool)

If true (default), remove duplicate xmlns attributes.

dtd(DTD)

The DTD. This is needed for SGML documents that contain elements with content model EMPTY. Characters which may not be written directly in the Stream's encoding will be written using character data entities from the DTD if at all possible, otherwise as numeric character references. Note that the DTD will NOT be written out at all; as yet there is no way to write out an internal subset, though it would not be hard to add one.

doctype(DocType)

Document type for the SGML document type declaration. If omitted it is taken from the root element. There is never any point in having this be disagree with the root element. A <!DOCTYPE> declaration will be written if and only if at least one of doctype(_), public(_), or system(_) is provided in Options.

public PubId

The public identifier to be written in the <!DOCTYPE> line.

system(SysId)

The system identifier to be written in the <!DOCTYPE> line.

header(Bool)

If Bool is 'false', do not emit the <xml ...> header line. (xml_write/3 only)

nsmap(Map:list(Id=URI))

When emitting embedded XML, assume these namespaces are already defined from the environment. (xml_write/3 only).

indent(Indent)

Indentation of the document (for embedding)

layout(Bool)

Emit/do not emit layout characters to make output readable.

net(Bool)

Use/do not use Null End Tags. For XML, this applies only to empty elements, so you get

    <foo/>      (default, net(true))
    <foo></foo> (net(false))

For SGML, this applies to empty elements, so you get

    <foo>       (if foo is declared to be EMPTY in the DTD)
    <foo></foo> (default, net(false))
    <foo//      (net(true))

and also to elements with character content not containing /

    <b>xxx</b>  (default, net(false))
    <b/xxx/     (net(true)).

Note that if the stream is UTF-8, the system will write special characters as UTF-8 sequences, while if it is ISO Latin-1 it will use (character) entities if there is a DTD that provides them, otherwise it will use numeric character references.