Link generated for chroma_sample_position is incorrect

[wantehchang]

This issue was originally reported in https://github.com/AOMediaCodec/av1-isobmff/issues/135#issuecomment-1668409438.

In the following sentence, the link generated for chroma_sample_position is incorrect:

The <dfn export>chroma_sample_position</dfn> field indicates the [=chroma_sample_position=] value from the [=Sequence Header OBU=].

We want to generate a link to the AV1 spec, but we end up generating a link to the chroma_sample_position term defined in this document.

I tried the following obvious fix, but it doesn't work:

diff --git a/index.bs b/index.bs
index 1eab014..3dc057e 100644
--- a/index.bs
+++ b/index.bs
@@ -108,6 +108,7 @@ url: https://aomediacodec.github.io/av1-spec/av1-spec.pdf#page=44; spec: AV1; ty
 url: https://aomediacodec.github.io/av1-spec/av1-spec.pdf#page=2; spec: AV1; type: dfn;
        text: buffer_removal_time
        text: byte_alignment
+       text: chroma_sample_position
        text: frame_presentation_time
        text: high_bitdepth
        text: initial_display_delay_minus_1

Cyril suggested using a for attribute in the dfn element in https://github.com/AOMediaCodec/av1-isobmff/issues/135#issuecomment-1686721917. I tried very hard but could not make it work. Hopefully someone more familiar with Bikeshed can figure out a fix.

[cconcolato]

Same for twelve_bit and high_bitdepth

[cconcolato]

We could simply remove the hyperlinks and say "as defined in AV1"