What common syntax errors can lead to unexpected errors like "Parse error: parse error, unexpected T_STRING" in PHP code?

One common syntax error that can lead to the "Parse error: parse error, unexpected T_STRING" in PHP code is mismatched quotes. This error usually occurs when there is a missing or extra single or double quote in the code. To solve this issue, make sure that quotes are properly matched and closed.

// Incorrect code with mismatched quotes causing parse error
echo 'Hello, world";
```

```php
// Corrected code with properly matched quotes
echo 'Hello, world';