Given the following HTML,
fruit cakes
<p>Christmas cakes</p>
the command
./tidy --show-body-only yes --quiet yes ~/goo.html
produces output
line 2 column 1 - Warning: plain text isn't allowed in <head> elements
line 2 column 1 - Info: <head> previously mentioned
fruit cakes
<p>Christmas cakes</p>
The initial warning seems very odd to me. Adding a body tag makes no difference and also generates another error:
fruit cakes
<body>
<p>Christmas cakes</p>
</body>
gives
line 2 column 1 - Warning: plain text isn't allowed in <head> elements
line 2 column 1 - Info: <head> previously mentioned
line 3 column 1 - Warning: discarding unexpected <body>
fruit cakes
<p>Christmas cakes</p>