<p>List of <a href="${link build-ref#labels}">labels</a>;
  <a href="#configurable-attributes">nonconfigurable</a>; default is <code>[]</code>
</p>

<p>
A list of
<code><a href="platforms-and-toolchains.html#constraint_value">constraint_values</a></code>
that must be present in the execution platform of this target's default exec
group. This is in addition to any constraints already set by the rule type.
Constraints are used to restrict the list of available execution platforms.

For more details, see
the description of
  <a href="/docs/toolchains#toolchain-resolution">toolchain resolution</a>.
  and
  <a href="/extending/exec-groups">exec groups</a>
  
</p>
