v1.15.4

ChainRulesCore v1.15.4

Diff since v1.15.3

Closed issues:

• Operations allowed on Tangent (#500)
• canonicalize should fill in NoTangent()? (#569)

Merged pull requests:

• Collapse zeros for Tuple & Ref tangents (#565) (@mcabbott)
• update to Documenter v0.27 (#572) (@oxinabox)
• Improve documentation of tangent types (#573) (@oxinabox)
• Take is_inplaceable_destination seriously (#577) (@mcabbott)
• Fix documentation around LaTeX commands (#583) (@hyrodium)