[#node-CoinbaseTx-witness]
= xref:node.adoc[node]::xref:node/CoinbaseTx.adoc[CoinbaseTx]::witness
:relfileprefix: ../../
:mrdocs:

The first (and only) witness stack element of the coinbase input&period;

== Synopsis

Declared in `&lt;node&sol;mining&lowbar;types&period;h&gt;`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
std::optional&lt;uint256&gt; witness;
----

== Description

Omitted for block templates without witness data&period;

This is currently the BIP 141 witness reserved value, and can be chosen arbitrarily by the node, but future soft forks may constrain it&period;


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