The following values are allowed: always, never, when-empty. Note, that all other values (including 1) work as never!
If the expression evaluates to always, TAB completion for XPath expressions always includes axis names.
If the expression evaluates to when-empty, the TAB completion list for XPath expressions includes axis names only if no element name matches the completion.
If the expression evaluates to never, the TAB completion list for XPath expressions never includes axis names.
The default value for this optio is always.
This command is equivalent to setting the $XPATH_AXIS_COMPLETION variable.