How I can make all the numbers in a string bold?
$st_nu = "Today123"
You can use a regular expression to bolden only numbers.
preg_replace('/(\d+)/', '<b>$1</b>', $st_nu);
What this does is matches any number 1 or more characters long, then surrounds it with the
<b> tag (bold).
Using your example, you'd get back the following: