clip-path="url(#…)" is never checked — no reference is registered with Reference.Type.SVG_CLIP_PATH #1678

Reference.Type.SVG_CLIP_PATH is defined, is assigned to ids, and is handled
in the checker — but nothing ever creates a reference of that type, so the
branch that would use it is unreachable and clip-path references go
unvalidated.

Where the type appears (5.3.0)

There is no registerReference(..., Type.SVG_CLIP_PATH) anywhere in
src/main/java. checkPaint() (OPSHandler.java:68) is called only for
fill and stroke (lines 237–238), and a case-insensitive search for
clippath/clip-path across src/main/java returns exactly one hit — the
id-typing at line 209. Nothing reads the attribute.

So clipPath is typed as a target only, and the two case SVG_CLIP_PATH
branches cannot be reached.

Effect

Two things go unreported. Both books below are a minimal EPUB 3 with one
XHTML document containing inline SVG; checked with epubcheck -u, 5.3.0.

1. A clip-path reference whose target is not a clipPath:

<svg xmlns="http://www.w3.org/2000/svg">
  <defs><linearGradient id="grad"><stop offset="0"/></linearGradient></defs>
  <rect clip-path="url(#grad)" width="5" height="5"/>
</svg>

→ no message. The equivalent mismatch through fill (fill="url(#sym)"
pointing at a <symbol>) is reported as RSC-014, so the intent seems to be
that this one would be too.

2. A clip-path reference to an id that does not exist:

<svg xmlns="http://www.w3.org/2000/svg">
  <defs><clipPath id="cp"><rect width="5" height="5"/></clipPath></defs>
  <rect clip-path="url(#nope)" width="5" height="5"/>
</svg>

→ no message. A dangling fill="url(#nope)" is RSC-012 in the same document.

(The CSS side does not cover it either: a stylesheet carrying
.a { clip-path: url(#nope) } is likewise silent.)

Not sure which fix you want

Registering clip-path in checkPaint-style would make both cases behave
like the paint ones. Alternatively, if clip-path references are deliberately
out of scope, the two case SVG_CLIP_PATH branches and the id-typing at
OPSHandler.java:211 are dead and could be removed.

Reported from work on an independent validator; happy to supply the sample
EPUBs if useful.