@Section
    @Title { Creating your own entry types and formats }
    @Tag { refstyles }
@Begin
@PP
Although the set of options to the @Code "@Reference" symbol
({@Code "@Tag"}, {@Code "@Type"}, {@Code "@Author"}, etc.) is fixed, you
can add your own reference types and change the formatting of existing types.
@PP
To do this you must be using your own setup file, as explained in
Section {@NumberOf setup}.  At the end of the setup file you will find
this line:
reference.print @Index { reference printing style }
ref.style @Index @Code "@RefStyle"
@ID @Code "@SysDatabase @RefStyle { refstyle }"
This tells Lout to consult a database file of reference styles called
{@Code "refstyle.ld"}.  These are not references, they are formatting
styles, one for each reference type.  The @Code "Sys" in @Code "@SysDatabase"
sys.database @Index @Code "@SysDatabase"
means that this file is stored in the @I { Lout system database directory },
system.database.dir @Index { system database directory }
refstyle.ld.file @Index { @Code "refstyle.ld" file}
which is where all the standard databases are kept.  To change the
formatting of a reference type, or to add your own types, you need to
create your own reference styles database file by copying and modifying
{@Code "refstyle.ld"}.
@PP
To find out the name of the Lout system database directory, type the
Unix command
@ID @Code "lout -V"
Then, supposing that the Lout system database directory is
{@Code "/usr/lout/data"}, type
@ID @Code "cp /usr/lout/data/refstyle.ld mystyle.ld"
to place a copy of the @Code "refstyle.ld" database file in your
mystyle.ld.file @Index { @Code "mystyle.ld" file}
directory, renaming it {@Code "mystyle.ld"}.  Since @Code "refstyle.ld"
is read-only, you may also need to change the mode of @Code "mystyle.ld"
to be writable (by @Code "chmod +w mystyle.ld" in Unix).  Now replace
@ID @Code "@SysDatabase @RefStyle { refstyle }"
at the end of your setup file by
@ID @Code "@Database @RefStyle { mystyle }"
and Lout will read its reference styles from @Code "mystyle.ld" instead
of {@Code "refstyle.ld"}.  Since the two are at
present identical, this has changed nothing so far; but now any changes
you make to @Code "mystyle.ld" will affect your document.  Changing
@Code "@SysDatabase" to @Code "@Database" makes Lout search your
current directory for {@Code "mystyle.ld"}, whereas @Code "@SysDatabase"
searches only the system directory.
@PP
In practice you will probably want to store your database of reference
styles in some library directory, so that it can be used by
many documents.  A Unix pathname is appropriate for this:
@ID @Code "@Database @RefStyle { \"/usr/jeff/lib/mystyle\" }"
Quotes are needed because of the @Code "/" characters.
@PP
The database entries within @Code "refstyle.ld" and @Code "mystyle.ld"
might look something like this:
@ID @OneRow @Code {
"{ Book @RefStyle @Style"
"  {  @Reference&&reftag @Open"
"     {"
"        @Author.  @I @Title.  @Publisher, @Year."
"     }"
"  }"
"}"
}
The meaning of the first two lines is beyond our scope, except that
@Code "Book" on the first line means that this is the entry which
defines how references of type @Code Book will be printed.  Fortunately,
apart from this one word these two lines are the same in every
reference style entry so you don't need to understand them.  The
important part is in the middle:
@ID @Code "@Author.  @I @Title.  @Publisher, @Year."
The meaning should be clear:  first print the author option and a full
stop, then the title option and another full stop in italics, and so
on.  To change the formatting of books, change this object.  To create
a new reference type, copy the entire database entry, change @Code Book
to a new name of your choice, and change the middle part.  Don't forget
to delete the index file @Code "mystyle.li" afterwards, if there is one,
so that Lout knows to generate it afresh.
@PP
Although the entry shown above is perfectly viable, the real entry for
@Code Book is much more complicated, in part because there are more
options than those basic four, but mainly because the real entry goes
to great lengths to do the right thing when options are omitted:
@ID @Tab
    vmargin { 0.45vx }
    @Fmta { @Col @Code A ! @Col @Code B }
{
@Rowa A { "{ Book @RefStyle @Style" }
@Rowa A { "  {  @Reference&&reftag @Open" }
@Rowa A { "     {" }
@Rowa A { "        {  @Author.  {}" }		B { "}  @If  @Author" }
@Rowa A { "        {  @I @Title" }		B { "}  @If  @Title" }
@Rowa A { "        {  @Word&&notitle" }		B { "}  @If  @Not @Title" }
@Rowa A { "        {  , @Pinpoint" }		B { "}  @If  @Pinpoint" }
@Rowa A { "        {  , @Word&&pages @NumSep @Pages" }	B { "}  @If  @Pages" }
@Rowa A { "        {  , @Word&&page @NumSep @Page" }	B { "}  @If  @Page" }
@Rowa A { "        {  .  @TitleNote" }		B { "}  @If  @TitleNote" }
@Rowa A { "        {  .  @HowPublished" }	B { "}  @If  @HowPublished" }
@Rowa A { "        {  .  @Publisher" }		B { "}  @If  @Publisher" }
@Rowa A { "        {  .  @Organization" }	B { "}  @If  @Organization" }
@Rowa A { "        {  .  @Institution" }	B { "}  @If  @Institution" }
@Rowa A { "        {  , @Address" }		B { "}  @If  @Address" }
@Rowa A { "        {  .  @Edition" }		B { "}  @If  @Edition" }
@Rowa A { "        {  , @Month @Year" }	B { "}  @If  @Year @And @Month" }
@Rowa A { "        {  , @Year " }	B { "}  @If  @Year @And @Not @Month" }
@Rowa A { "        {  ." }		B { "}  @If  @True" }
@Rowa A { "        {  {}  URL @URL." }	B { "}  @If  @URL" }
@Rowa A { "        {  {}  @Note" }	B { "}  @If  @Note" }
@Rowa A { "     }" }
@Rowa A { "  }" }
@Rowa A { "}" }
}
The meaning is that each object to the left of an @Code "@If" will be
if. @Index @Code "@If"
printed only if the condition to the right of the @Code "@If" is
true.  The condition may contain options, which are considered to be
true if they are not omitted (non-empty), and it may contain {@Code "@And"},
and. @Index @Code "@And"
or. @Index @Code "@Or"
not. @Index @Code "@Not"
true. @Index @Code "@True"
{@Code "@Or"}, {@Code "@Not"}, and @Code "@True" with the usual precedence
and meaning.  Sub-conditions may be enclosed in braces if desired, although
it is best to keep the conditions as simple as possible given the
complexity of the whole setup.
@PP
The objects subject to @Code "@If" are printed with no space preceding
them; any space in the final print will be the result of space within
them, not between them.  This is why @Code "@If @True" is not redundant.
@PP
The object @Code "@Word&&notitle" produces @Code "No title" in the
current language; @Code "@Word&&pages" produces {@Code pages} in the
current language, and so on.  Consult database @Code "standard.ld" for
standard.ld.file @Index { @Code "standard.ld" file }
other standard words and phrases, and page {@PageOf numsep} for
{@Code "@NumSep"}.
@End @Section