Formatting parsed data

When parsing SGML or XML data, the parsed data can be formatted in one of two approaches. The first approach is to capture the parsed data in an OmniMark string and then use regular OmniMark programming techniques to format the data. The other is to give instructions to OmniMark on how the data should be formatted. The latter approach is often faster and cleaner.

OmniMark can be instructed on how to format data using format items and placing the appropriate format modifiers on the format commands %c, %v, and %q.

Formatting data content

Unless intercepted in a data-content rule, the parser outputs data content to the current output scope. Format modifiers can be added to the parse continuation operator, %c, to change how the data content is formatted.

The following modifiers are supported.

  • The h modifier prevents line-breaking rules (insertion-break and replacement-break) from applying to the content of the current component.
  • The l modifier converts all text to lowercase. It only applies to letters in the processed document (data characters in content and attribute values) copied from the input to the output. It does not apply to letters in quoted strings in the OmniMark program.
  • The u modifier converts all of the text to uppercase. It only applies to letters in the processed document (data characters in content and attribute values) copied from the input to the output. It does not apply to letters in quoted strings in the OmniMark program.
  • The s modifier causes white space to be stripped in the processed content.
    1. Leading and trailing spaces and line-ends are removed from components.
    2. Sequences of tabs and spaces are condensed to a single space.
    3. Sequences of line-ends, together with any intervening, leading, or trailing tabs and spaces, are condensed to a single line-end.
    The s modifier affects only text received directly from the SGML or XML parser, or from characters specified with format items that explicitly allow stripping.
  • z modifier turns off translate rules that would otherwise apply to all or part of the content.

It is possible to override the subcomponents, even those going into the same stream, by removing modifiers with the following syntax: 

  put my-stream with "" "%c"

Formatting element names and external entities

The %q format item refers to the name of the currently opened element everywhere except in external-text-entity and external-data-entity rules. In functions, even if the function is called from an external-text-entity or an external-data-entity rule, %q still refers to the currently opened element. This is to ensure that a function always behaves in the same way, regardless of what rule it is called from.

When referring to an element, a number of modifiers can be used to change the default behaviour of %q.

  • The l modifier converts all text to lowercase; it cannot be used with the u modifier.
  • The u modifier converts all text to uppercase; it cannot be used with the l modifier.
  • The f modifier, the field width modifier, is allowed with the %q format. The f modifier must be preceded by a positive number. If the specified number is less than the minimum number of characters needed to format the value, the modifier is ignored. If it is greater, space characters are added to the right of the value to fill it out to the field width.
  • The k modifier is allowed only with the f modifier: it modifies the behaviour of f to put the spaces to the left of the element name, instead of to the right.

%q refers to the name of the current entity in the body of an external-data-entity or an external-text-entity rule. Anywhere else, it refers to the current element.

When referring to an entity, a number of modifiers can be used to change the default behaviour of %q.

  • The e modifier causes OmniMark to access the system identifier from the entity declaration instead of the entity name.
  • The o modifier causes OmniMark to access the notation name from the entity declaration instead of the entity name. This modifier can only be used in external-data-entity rules because external text entities do not have a notation. This is the only format modifier that can be combined with the f or k format modifiers, described above.
  • The p modifier causes OmniMark to access the public identifier from the entity declaration instead of the entity name.

These modifiers can also be used in combinations.

  • The combination ep causes OmniMark to access the system identifier obtained by searching for the entity's public identifier on the #library shelf.
  • The combination eo causes OmniMark to access the system identifier declared for the notation associated with the entity. This combination can only be used in an external-data-entity rule because external text entities do not have notations.
  • All three can be combined, eop; this causes OmniMark to access the system identifier obtained by searching for the entity notation's public identifier on the #library shelf. This combination can only be used in an external-data-entity rule because external text entities do not have notations.

If an entity does not have a system identifier, then the e format modifier acts the way ep does.

If an entity does not have a public identifier, or if the #library shelf does not have an entry whose key is the public identifier, then it is an error to use the ep format modifier combination. If such an entity also does not declare a system identifier in the entity declaration, then it is also an error to use the e format modifier. The same observation applies to the system identifier of the entity's notation when using the above format modifiers in combination with the o format modifier.

All of the combinations above may be further combined with the l or u format modifiers. Additionally, the o format modifier can also be combined with the f and k format modifiers, provided that it is not also combined with the e or p modifiers.

The f and k format modifiers can only be used with entity names and notation names.

Formatting attributes and external data entities

The %v format item is used to output an attribute of an element or of an external-data-entity.

The following example outputs the section identifier (the attribute named ID) when processing an SGML document: 

  element "section"
     output "Section: %v(ID) %c"

The DTD for the above example must contain lines similar to the following: 

  <!element section - o (#pcdata)>
  <!attlist section id number #required>

In element rules, the named attribute must be an attribute of the element; in external-data-entity rules, it must be a data attribute of the entity being processed. When %v is used in any other context, the named attribute must be an attribute of the containing element.

A number of modifiers can be used to change the default behaviour of %v.

  • The l modifier forces the letters in the attribute value to lowercase.
  • The u modifier forces the letters in the attribute value to uppercase.
  • The f modifier, the field-width modifier is allowed in the %v format; it is ignored for cdata. The f modifier must be preceded by a positive number. If the number is less than the minimum number of characters needed to print the attribute value, it is ignored. If it is greater, space characters are added to the right of the value to fill out the field width.
  • The k modifier is allowed only with f: it changes the behaviour of f to put the spaces to the left of the value instead of to the right.

In addition to the above modifiers, the modifiers below can be used if the attribute is declared as cdata.

  • The h modifier prevents the insertion of line breaks.
  • The s modifier minimizes white spaces, as follows:
    1. sequences of white space not containing a line-end are compressed to a single space, and
    2. sequences of white space containing a line-end are compressed into a single line-end.
  • The z modifier prevents selection of any translate rules that would otherwise apply to all or part of the attribute value.

If the attribute's declared type is entity or entities, and the entity name refers to an external entity, you can use the following modifiers (but not with the f, k, l, and u modifiers):

  • The e modifier causes OmniMark to access the system identifier from the entity declaration instead of accessing the entity name.
  • The o modifier causes OmniMark to access the notation name from the entity declaration instead of from the entity name. In this case, the f, k, l, and u modifiers can be used.
  • The p modifier causes OmniMark to access the public identifier from the entity declaration instead of accessing the entity name.

These modifiers can be combined.

  • The combination ep causes OmniMark to access the system identifier, as obtained by using the entity's public identifier to index into the #library shelf.
  • The combination eo causes OmniMark to access the system identifier declared for the notation associated with the entity.
  • The combination pov causes OmniMark to access the public identifier declared for the notation associated with the entity.
  • The combination epov causes OmniMark to access the system identifier, as obtained by using the entity notation's public identifier to index into the #library shelf.

If an entity has no system identifier, then e acts as ep does. It is an error if either e or ep is used and a system identifier cannot be obtained using the #library shelf.

This format accesses letters within system and public identifiers in uppercase or lowercase as they appear in the entity declaration. Letters in element, entity, or notation names appear in uppercase or lowercase as they appear in the processed document, unless the SGML declaration specifies uppercase substitution for that class of name. If so, the name is accessed with letters forced to uppercase. Thus, in the Reference Concrete Syntax, by default, element and notation names appear in uppercase while entity names appear as entered in the document.

For an entities attribute, if the attribute value contains more than one entity name, the using prefix must be used to select one entity whose system or public identifier is to be manipulated or displayed.

If the value of an entity or entities attribute is the name of an internal cdata or sdata entity, the %ev format can be used to determine the replacement text of the internal entity.

The e, p, and ep formats can also be used with notation, under the same conditions as entity or entities.

This example illustrates how the %ev format handles internal and external entities differently.

The element as-is has a single required ENTITY attribute text. The entity named by the attribute value provides the text that is to replace the element, wherever it occurs in a document. 

  <!element as-is - o empty>
  <!element as-is text entity #required>

The element rule for processing the as-is element does the following:

  • If the entity named by attribute text is an external entity, then the element rule uses the system identifier declared for the entity, or the system identifier found by indexing the #library shelf with the entity's declared public identifier, as a filename, and replaces the element with the contents of the file. (OmniMark reports an error if the entity does not have a system identifier and does not have a public identifier mapped to a system identifier, or if the system identifier names a nonexistent file. This may or may not be appropriate for a particular OmniMark program.)
  • If the entity is an internal entity, then the element rule uses the replacement text of the internal entity and replaces the element with that text.

Note that %ev returns one of two things, depending on whether the entity named by the attribute to which it is applied is internal or external.

  • For an attribute token that is the name of an external entity, it returns the system identifier.
  • For an attribute token that is the name of an internal entity, it returns that entity's replacement text. 

  element "as-is"
     do when attribute text is external
        output file "%ev(text)"
     else
        output "%ev(text)"
     done
  
     suppress

Prerequisite Concepts
Related Topics