Attribute stamped on each panel's root <svg> in multi-panel mode; its
value is the panel index. Emitted selectors use it as an ancestor segment
so one panel's selectors can never match another panel's marks, and
MaidrSubplot.selector targets it for subplot-level highlighting.
Attribute stamped on each panel's root
<svg>in multi-panel mode; its value is the panel index. Emitted selectors use it as an ancestor segment so one panel's selectors can never match another panel's marks, andMaidrSubplot.selectortargets it for subplot-level highlighting.