What is the output of `echo 5 * '10px';`?

In this case, the output of echo 5 * '10px'; is indeed 50. When PHP encounters the expression for multiplication, it will first attempt to convert the string operand ('10px') into a numeric value.

PHP performs type juggling, which means that it tries to interpret the string in a way that makes sense in a numeric context. The conversion will stop at the first non-numeric character it encounters. In the string '10px', the numeric portion is 10, and the conversion will disregard anything after that, which is why the string is treated as the numeric value 10.

Therefore, the calculation proceeds as follows:

5 (the integer) multiplied by 10 (the parsed part of the string) results in 50. This demonstrates the behavior of PHP regarding type casting and string conversion in arithmetic contexts, which is crucial for understanding how PHP handles such operations.