src/Doc/System/Sessions.thy

 text \<open>The @{tool_def build} tool invokes the build process for
   Isabelle sessions.  It manages dependencies between sessions,
   related sources of theories and auxiliary files, and target heap
   images.  Accordingly, it runs instances of the prover process with
   optional document preparation.  Its command-line usage
-  is:\footnote{Isabelle/Scala provides the same functionality via
-  \<^verbatim>\<open>isabelle.Build.build\<close>.}
+  is:\<^footnote>\<open>Isabelle/Scala provides the same functionality via
+  \<^verbatim>\<open>isabelle.Build.build\<close>.\<close>
   @{verbatim [display]
 \<open>Usage: isabelle build [OPTIONS] [SESSIONS ...]
 
   Options are:
     -D DIR       include session directory and select its sessions