Texinfo processors create tag tables automatically. The only exception
arise when texinfo-format-buffer is called with a prefix, as
C-u M-x texinfo-format-buffer, to create an non split Info
file without a tag table (which can be useful in some cases for Info file
validation, see Creating an Unsplit File and Adding a Tag Table). Adding a tag table is therefore
more generally useful for manually written Info files.
To create a tag table for an nonsplit file, visit the Info file you wish to tagify and type:
M-x Info-tagify
(Note the uppercase ‘I’ in Info-tagify.) This creates an
Info file with a tag table. A tag table is part of a well formed Info
file (see Tag Files and Split Files). A tag table is also needed to validate
or split the Info file.