Lout 3.27 tag.3.27

git-svn-id: http://svn.savannah.nongnu.org/svn/lout/tags/3.27@24 9365b830-b601-4143-9ba8-b4a8e2c3339c

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+Basser Lout Version 3 and the PostScript Document Structuring Conventions
+Jeffrey H. Kingston
+24 March 1994
+Modified to explain changes in font inclusion, 3 June 2000
+
+The following notes detail all areas known to the author where Lout does
+not fully conform to Version 3.0 of the PostScript Document Structuring
+Conventions (DSC), as given in Appendix G of the PostScript Language
+Reference Manual, second edition (PLRM).  Page numbers refer to PLRM.
+These are minor infringements which should not trouble anyone (I hope).
+Please let me know of any problems.
+
+Language level and extensions.  Lout does not produce %%LanguageLevel and
+%%Extensions comments, implying that its output is Level 1 PostScript with
+no extensions (p644).  This is true except for PostScript which user-level
+commands choose to add via @SetColour, @Graphic, @IncludeGraphic, and
+@PrependGraphic commands.  If this added PostScript is not Level 1 then
+the absence of %%LanguageLevel and %%Extensions comments will be in
+violation of the DSC.  Lout's standard packages use only Level 1, which
+should take care of most of the @SetColour, @Graphic, and @PrependGraphic
+commands encountered in practice.  If a %%LanguageLevel or %%Extensions
+comment is encountered in an @IncludeGraphic file, Lout prints a warning
+message but takes no other action.
+
+Color separation conventions (pp685-688).  At present Lout generates none
+of the comments described in this section.
+
+DocumentSuppliedResources.  According to p671, each included document
+(%%Begin(End)Document pair in PostScript, @IncludeGraphic file in Lout)
+should have a corresponding "%%DocumentSuppliedResources: file" entry.
+This contradicts p660, where each %%DocumentSuppliedResources entry is
+said to correspond to a %%Begin(End)Resource pair.  Lout does not record
+%%Begin(End)Document pairs in the %%DocumentSuppliedResources list.
+
+EOF.  According to p673, the %%EOF comment of an included document (i.e.
+one enclosed in %%Begin(End)Document) will be ignored.  However, p658
+does not mention this exception, and one Adobe PostScript interpreter at
+least in the author's environment terminates at the first %%EOF whether
+or not it lies inside %%Begin(End)Document.  Accordingly, Lout strips
+out any %%EOF comment within any included document during inclusion.
+
+Font inclusion.  According to p678, "%%IncludeResource: font" comments
+relating to commonly available fonts should be placed in the document
+setup section.  However no definition of which fonts fall into this
+category is offered, so this requirement is not observed by Lout.
+Instead, Lout generates one "%%IncludeResource: font" in the page setup
+section for each font used on the corresponding page.  (It used to be
+the case that fonts used on the first page were an exception to this
+rule; they were done once only in the document setup section.  This
+exception has been removed from Lout Version 3.22 and above.)  Thus,
+fonts used on many pages will generate many "%%IncludeResource: font"
+comments, one for each page on which the font is used, which in turn
+implies that these fonts might be downloaded many times (Lout itself
+never downloads any font, but a document manager might react to an
+"%%IncludeResource: font" comment by doing so).  However, most fonts
+used by most people are already in the printer, and in these cases
+"it is highly likely that the font server or document manager would
+ignore the inclusion request, because the font would already be
+available on the printer" (p678).  The rationale for putting all
+"%%IncludeResource: font" comments into page setups is that it gives
+document managers exact information about what fonts are used on
+each page, which, hopefully, they can put to good use.
+
+PageResources.  This comment is supposed to list all resources needed
+or supplied on the current page except for procsets (p685).  At present
+Lout lists fonts but not encoding vectors under this comment.
+
+Definitions in EPS files.  On p736, "it is strongly recommended that an
+EPS file make its definitions in its own dictionary or dictionaries".
+Lout -EPS does not follow this recommendation, since it is not clear where
+to create this dictionary or dictionaries, given that the DSC states (p625)
+that the prolog should be a sequence of procset definitions (after the
+header section and defaults section) only.  Perhaps each procset should be
+in its own dictionary, as is done in lout/include/fig_prepend for example,
+but this is not stated anywhere.