minor updates to the AS5 spec, mostly general cleaning and rewordings

Originally committed to SVN as r1407.

specs/as5/as5.tex

@@ -102,31 +102,33 @@ termination mark; they always end at the start of the next one or at the end of
 \emph{Section names are case sensitive.}
 
 Each section is divided in lines, each line representing one command or definition. Empty
-lines \must\ be ignored. It is recommended that programs generating AS5 files insert
-a blank line at the end of each section to increase readability. There \must\ always
-be a blank line at the end of the file (as every line is required to end in a line break).
+lines (that is, lines only containing a line ending) \must\ be ignored by the parser.
+It is recommended that programs generating AS5 files insert a blank line at the end of each
+section to increase readability. There \must\ always be a blank line at the end of the file
+(as every line is required to end in a line break).
 
 Each line in a section takes the general form of \textit{Type: data1,data2,...,dataN}. An
-unknown \textit{Type} \must\ be ignored by a parser. It is recommended that subtitle
-editing programs keep such ignored lines in the file after re-saving it. Note that the space
-after the colon is \emph{mandatory}.
+unknown \textit{Type} \must\ be ignored by a parser. Subtitle editing programs \should\ keep
+such ignored lines in the file after re-saving it. Note that the space after the colon is \emph{mandatory}.
 
 There are two sections which are required, \emph{[AS5]} and \emph{[Events]}, the former being
 the equivalent of \emph{[Script Info]} in previous formats. If either of those sections is
-missing, the file is deemed invalid and \emph(MUST) be refused by the parser. Any other section
+missing, the file is invalid and \emph(MUST) be refused by the parser. Any other section
 can be ommitted from the file, and need not be implemented by all parsers. However, any unknown
 section \must\ be preserved in the file by a subtitle editing program when it re-saves a
 file with sections that it does not recognize. It can, however, be removed at the user's discretion.
 
 Finally, there is a special type of undefined group, \emph{[Private:PROGNAME]}, which 
 \must\ be \emph{ENTIRELY} preserved by other programs when re-saving it. This is used to
-store program-specific data, for example, Aegisub would create a group called
+store program-specific data. For example, Aegisub would create a group called
 \emph{[Private:Aegisub]} to store its data inside. This type of group should be identified
 by the fact that it starts with \emph{"`[Private:"'}.
 
+The sections \may\ be written in any order, with the exception of the \emph{[AS5]} section which
+\must\ always be the first section.
 
 \subsubsection{[AS5]}
-This must be the first section in every AS5 file. If the very first line of the file is not
+This \must\ be the first section in every AS5 file. If the very first line of the file is not
 [AS5], the file \must\ be rejected by the parser as invalid. Note, however, that the first
 line is allowed to contain a Byte-Order Mark (BOM), which is the character U+FEFF encoded in
 the encoding used for the rest of the script\cite{Unicode BOM}. The first four bytes will therefore be:
@@ -155,10 +157,10 @@ video resolution, however, subtitles \must\ be rendered on such a coordinate spa
 640x480 script, \textbackslash{pos(320,240)} always represents the center of the script, no matter the
 resolution of the video it's being drawn on. Also, in a 100x100 script, a radius 50 circle centered on
 the center will always take half of the height and half of the width of the video, even if that means
-being distorted if drawn on a 640x480 video.
+being distorted if drawn on a video with a non-1:1 aspect ratio (for example, a 640x480 video).
 \end{itemize}
 
-Also, the following items are not required, but are recommended. They all have default values:
+The following items \may\ also be used; they are not required, but are recommended. They all have default values:
 
 \begin{itemize}
 \item Generator: The name of the program that generated this script, e.g. \textit{"`Generator: Aegisub"'}.
@@ -172,14 +174,15 @@ even if it means that the line will become unreadable because it goes outside th
 no extensions available. Renderers should read this to enable any extensions that they might support.
 Editing programs \must\ keep this field intact, unless the user chooses otherwise. Scripts WILL break
 if the list of extensions is suddenly lost.
-\item Credits: Credits for the people who worked on this subtitle file. Should be ignored by the renderer.
-\item Title: The title of this script. Should be ignored by the renderer. Subtitling programs may opt to display
-this title to the user.
+\item Credits: Credits for the people who worked on this subtitle file. Purely for informational purposes and
+\should\ be ignored by the renderer. Subtitling programs \should\ be able to display these credits to the user.
+\item Title: The title of this script. Purely for informational purposes and \should\ be ignored by the renderer.
+Subtitling programs \should\ be able to display this title to the user.
 \end{itemize}
 
-Although any other lines are allowed in this group, this is not encouraged, as they might conflict
-with future revisions of the format. Instead, they should be stored in \textit{[Private:PROGNAME]} groups,
-as mentioned above.
+Unlike in the previous incarnations of the format, storing private data here is not allowed, which means
+that this section \must not\ contain any properties not listed here. Any application-specific or otherwise
+private data \must\ be stored in \textit{[Private:PROGNAME]} groups instead, as mentioned above.
 
 
 \subsubsection{[Events]}
@@ -195,26 +198,29 @@ time is \emph{inclusive}.
 \item End: The end time of the line. It follows the same format as the start time. The line is only
 displayed if the timestamp of the current frame is \emph{lesser than} the end time. That is, end time is
 \emph{exclusive}. In particular, it means that a line whose start time is equal to its end time will
-never be displayed. If the end time is lesser than the start time, the renderer may issue a warning,
-but should render the remaining lines regardless of the issue.
-\item Style: The name of the default style used for this line. See the [Style] section below. Should be
-left blank if you want to use the the script's global default style. If an unknown style is specified,
-the renderer \must\ fallback to default, and might issue a warning.
+never be displayed. If the end time is earlier than the start time, the renderer \may\ issue a warning,
+but it \should\ render the remaining lines regardless of the issue.
+\item Style: The name of the default style used for this line. See the [Style] section below. If left blank,
+the script's global default style \must\ be used. If an unknown style name is specified, the renderer \must\
+fallback to default, and \may\ issue a warning.
 \item User: This field is used by the program to store program-specific data in each line. Renderers
-should ignore this. This should be left blank if it's not used.
+\should\ ignore this (but \may\ use it for application-specific extension features). This field \should\
+be left blank if it's not used. Note that whatever data is stored here \must not\ contain any commas!
 \item Content: The actual text of the line. This contains actual text and override tags. See the section
 on override tags for more information.
 \end{itemize}
 
 The timestamp format is h...h:mm:ss[.s...], that is, it begins with an integer of arbitrary length
 (up to a maximum of 4 digits) representing the number of hours, followed by a one-digit or two-digit integer
-representing minutes, and a floating point number representing seconds. Localization is irrelevant: a
-period ("`."') is always used to separate the decimal point. This way, 0:21:42.5 and 0000:21:42.5000 are
-equivalent, and both represent 0 hours, 21 minutes, 42 seconds and 500 miliseconds.
+representing minutes, and a floating point number representing seconds. Leading zeroes in the hours field \may\
+be ommitted. Localization is irrelevant: a period ("`."') is always used to separate the decimal point.
+This way, 0:21:42.5 and 0000:21:42.5000 are equivalent, and both represent 0 hours, 21 minutes, 42 seconds
+and 500 miliseconds.
 
 Spaces between each field \must\ be ignored by all parsers. Any spaces at the beginning of the
-content line should be stripped. A hard space or empty override block should be used if space at the
-start of a line is truly desirable. That is, the two following lines are identical:
+content line \should\ be stripped by any editing program. A hard space (see the overrides section) or empty
+override block should be used if space at the start of a line is truly desirable. That is, the two
+following lines are syntactically identical:
 
 \begin{verbatim}
 Line:  0:2:31.57  ,  0:02:34.22  ,  ,  ,  Hello world of {\b1}AS5{\b0}!
@@ -230,8 +236,8 @@ simplified when compared to the previous formats, and now contains only three fi
 
 \begin{itemize}
 \item Name: The name of this style. Style names are not case-sensitive, but \must\ be unique. A
-script with conflicting style names must be refused by the parser. If the style name is "`Default"', it
-will be used for all lines that ommit the style name. If there is no "`Default"' line, the renderer
+script with conflicting style names \must\ be rejected by the parser. If the style name is "`Default"', it
+will be used for all lines that omit the style name. If there is no "`Default"' line, the renderer
 default is used.
 \item Parent: The style from which the current style derives from. See below for more information.
 Leaving this field blank means that the style derives from the renderer's default style.
@@ -282,6 +288,10 @@ Style: Actor2,,\fn(Respublica)\fs24\bord2\shad2\4a#80\2c#000000\1c#FFB3CF
 Since all that deriving a style from another does is append the new tags to the end of the previous,
 this way of declaring styles is identical to the one above, but is more verbose.
 
+If no Default style is defined, the renderer \must\ choose its own defaults to render the text with.
+These are entirely arbitrary and can be set to anything, but the renderer \should\
+let the user set his own defaults.
+
 \addcontentsline{toc}{section}{References}
 \begin{thebibliography}{1}