Parser options, which are entered after the volume name, are passed directly to the parser, which is the part of the HelpTag software that converts your marked-up files into a run-time file.
These options can be applied in the following ways:
Entered on the command line after the volume name
Listed in a file named helptag.opt located in the current directory
Listed in a file named volume.opt in the current directory
Options entered on the command line override those options that may have also been set using a different method.
Specifies whether the dthelptag command should continue if a parser error is encountered. The default is onerror=stop, which causes the command to stop even if one parser error is encountered. If you specify onerror=go, processing will continue, but the created run-time help file may not work properly.
Specifies which character set was used to author the text files. The correct character set name is needed to ensure that the help topics are displayed in the proper font. The default is charset=ISO-8859-1. You can also specify a character set within your help volume by declaring an entity named LanguageElementDefaultCharset. The /usr/dt/dthelp/dthelptag/helplang.ent file includes this entity declaration. See Chapter 14, Native Language Support, for a list of supported character sets.
Adds another directory to the list of directories that are searched to find referenced file entities. To specify multiple directories, use multiple search=directory options. If no search options are used, only the current directory is searched.
Ignores the list of search directories. This option is useful in the command line to override search options specified in the helptag.opt file.
Causes author's memos (which are entered using the <memo> element) to be included. The default is nomemo, which causes HelpTag to ignore memos.
Causes HelpTag to ignore author's memos (which are entered with the <memo> element). This is the default.
dthelptag (1) man page