src/main/java/com/google/devtools/build/docgen/templates/attributes/common/toolchains.html

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

<p>
  The set of targets whose <a href="${link make-variables}">Make variables</a> this target is
  allowed to access. These targets are either instances of rules that provide
  <code>TemplateVariableInfo</code> or special targets for toolchain types built into Bazel. These
  include:

<ul>
    <li><code>@bazel_tools//tools/cpp:current_cc_toolchain</code>
  <li><code>@bazel_tools//tools/jdk:current_java_runtime</code>
  </ul>

<p>
  Note that this is distinct from the concept of
    <a href="/docs/toolchains#toolchain-resolution">toolchain resolution</a>
    that is used by rule implementations for platform-dependent configuration. You cannot use this
  attribute to determine which specific <code>cc_toolchain</code> or <code>java_toolchain</code> a
  target will use.
</p>