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Option values for each group are stored as a list of option assignments. This list does not have to contain every supported option. Values for options missing from this list are taken from the default option values.
To manipulate the list of option values for the groups, you use the
\hlopts and \hldestopts commands with an optional
argument:
\hlopts[groups]{options}
\hldestopts[groups]{options}
\hlopts![groups]{options}
\hldestopts![groups]{options}
where groups is a comma-separated list of groups and
options is a comma-separated list of option assignments. The
two special “groups”, the empty group and the star (`*')
group, have the same meaning as for \hltype and
\hldesttype.
When used without the exclamation mark, \hlopts and
\hldestopts preserve the current list of options for the groups,
and only update the options listed in options. If you add the
exclamation mark, the current list of options for each group in
groups is discarded and the new list is set to options.
The “overriding” nature of the `!' is appropriate when you give a complete specification of the options for a group, e.g., at the beginning of your document. On the other hand, when you want to adjust some option(s) and leave others intact, you should use the macros without the `!'.
For example, with displayed mathematical formulas, you often need to
adjust the `raise' option for the
`eq' destgroup, because the formulas often contain large parentheses and
brackets. But when doing so, you want to leave the other settings
unchanged. To achieve this, call \hldestopts without the
`!', for example:
$$\hldestopts[eq]{raise=2.5\normalbaselineskip}
...
$$
The display commands (`$$') implicitly put the entire
formula inside a (TeX) group (\begingroup...\endgroup), so
you do not need to isolate the setting of the `raise' option—it
will be restored after the closing `$$'.
Initially, Eplain sets the option lists for almost all groups to empty, so that the groups fall back on the default values for all options. The one exception to this rule is the `eq' destgroup, whose initial option list contains one setting:
raise=1.7\normalbaselineskip
This setting usually accommodates the large operators, which often appear in displayed math.