Names the element to which the reference is pointing
The values may be used to control type-specific processing or validation.
<!ENTITY % ref-types "aff | app | author-notes | bibr |
boxed-text | chem-struct-wrapper | contrib | corresp | disp-formula | fig | fn | kwd | list |
plate | scheme | sec | statement | supplementary-material | table | table-fn |
other" >link.ent