There (mostly) can't be statements outside of namespaces
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<?php
echo 1;
namespace A;
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Namespace declaration statement has to be the very first statement in the script on line 3
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<?php
namespace A {}
echo 1;
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No code may exist outside of namespace {} on line 3
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<?php
namespace A {}
declare(ticks=1);
namespace B {}
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No code may exist outside of namespace {} on line 3