Riddle Poem: It can be a celebrity and nothing at once

I just wrote this poem. I hope you guys like it.

This thing can be so tiny,
That's when it has the most variety.

Standing up straight it is surrounded,
Otherwise it can make things bounded.

Within a box it lets you choose,
But if it points up you will lose.

It can be seen leaning,
That's when it reveals true meaning.

It can be a celebrity and nothing at once,
It can show uncertainty but never incoherence.

But when wealth is what it shows,
The end is what you will know.

What is the poem referring to? Can you explain what each line means?

Answer

I think it's

Regular Expression Syntax

This thing can be so tiny, That's when it has the most variety.

The . character is a wildcard which can match ANY single character.

Standing up straight, it is surrounded, Otherwise it can make things bounded.

The | character is an "or" operator, so it's surrounded by two choices. Otherwise (if not standing up, but on its side) it sets the bounds of a range, e.g. [a-z]

Within a box it lets you choose,

The box is []. [bc]at returns bat or cat, in other words you choose between the characters within the box.

But if it points up you will lose.

[^bc]at will return ANYTHING OTHER than bat or cat. You lose these options.

It can be seen leaning, That's when it reveals true meaning.

\ combines with other characters to create something other than a literal character. For example, \t is a tab character

It can be a celebrity and nothing at once,

The "star" character * matches any string with zero or more of a given element.

It can show uncertainty but never incoherence.

You might not be certain if you've written the regular expression without errors, which matches what you're looking for, but either way what's returned is coherent with what you wrote. Not too sure about this one...

But when wealth is what it shows, The end, you will know.

$ matches the end position of a string.