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 | contrib | corresp |
disp-formula | fig | fn | kwd | list |
plate | scheme | sec | statement |
supplementary-material |
table | table-fn |
other" >link.ent