A problem about variablefunction

In a variablefunction issue Manual, echo, print is not a real function, so variablefunction cannot be applied. But I tried PHPcode $ t = 'echo '; $ t ('000000');, this ...... Is it useful? I usually have a straight variable function problem.
In the manual, echo and print are not real functions, so variable functions cannot be applied. But I tried it.

PHP code

  $ T = 'echo '; $ t ('20140901 ');

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This ...... Is it useful? Generally, echo "XXX --> $ X \ n"; or echo ("XXX") has the same effect.
As long as it can be output.
It seems that many details are ignored at ordinary times ......
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Is the landlord running. Is that true?
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$ T = 'echo ';
$ T ('000000 ');
Fatal error: Call to undefined function echo ()...