I am unsure how to use keys in the declaration of environments.  How<br>does one handle the case when the user supplies or does not supply<br>the key-value pairs ?<br><br>    \documentclass[a4paper,10pt]{article}<br>    <br>    \ExplSyntaxOn<br>    <br>    \tl_new:N \tlapis_kl_tl<br>    \tl_new:N \tlapis_lv_tl<br>    <br>    \keys_define:nn { tlapis_keys }<br>      {<br>        kl .tl_set:N = \tlapis_kl_tl,<br>        kl .default:n = {red},<br>        kl .initial:n = {red},<br>    <br>        lv .tl_set:N = \tlapis_lv_tl,<br>        lv .default:n = {},<br>        lv .initial:n = {},<br>      }<br>    <br>    \NewDocumentEnvironment {wvTlapis} { o }<br>        {<br>          \tl_if_novalue:nF {#1}<br>            { \keys_set:nn {tlapis_keys} {#1} }<br>        }<br>      { }<br>    <br>    \ExplSyntaxOff<br>    <br>    \begin{document}<br>    <br>    <br>    \end{document}<br><br><br><br><br><br>