(eplain.info)Converting to characters

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7.5 Converting to characters
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Eplain defines '\xrlabel' to produce control sequence names for
cross-reference labels, et al. This macro expands to its argument with
an '_' appended. (It does this because the usual use of '\xrlabel' is to
generate a control sequence name, and we naturally want to avoid
conflicts between control sequence names.)

   Because '\xrlabel' is fully expandable, to make a control sequence
name out of the result you need only do

     \csname \xrlabel{LABEL}\endcsname

The '\csname' primitive makes a control sequence name out of any
sequence of character tokens, regardless of category code. Labels can
therefore include any characters except for '\', '{', '}', and '#', all
of which are used in macro definitions themselves.

   '\sanitize' takes a control sequence as an argument and converts the
expansion of the control sequence into a list of character tokens. This
is the behavior you want when writing information like chapter titles to
an output file. For example, here is part of the definition of
'\writenumberedtocentry'; '#2' is the title that the user has given.

     ...
     \def\temp{#2}%
     ...
       \write\tocfile{%
         ...
         \sanitize\temp
         ...
       }%