I don't mean manacles or chains. Or dungeons.

But other kinds of constraints apply a kind of pressure that may make the poet surprise her or himself. Think what Shakespeare did inside iambic pentameter, and Thom Gunn inside syllabic forms.

The WrapperRhyme challenge offered some old constraints and some new ones, and it's been fascinating to see how writers responded to these.

Rhyming, for example, is one of the oldest constraints. Generally, I'd say poets are less good at it than they used to be (with notable exceptions) because it's not one of the main tools of contemporary poetry. But still some lovely examples of super-rhyme have arrived here, and I've been tweeting or instagramming some of them.

But simply writing on a wrapper is in itself a constraint. Much of the wrapping material used for confectionery, for example, is that silvery slippery stuff that welcomes no pen. There are pens that will write on it, but you have to go to some lengths to find them. My implement of choice is Staedtler Lumocolor Marker Pen Permanent Special from Cult Pens. (I am on my fourth pen.)

Crisps and savoury snacks are usually bagged in the same silvery stuff but with an added element of grease at which even the Lumocolor Marker Pens jib. You have to wash the wrapping in soapy water (or at least you could, depending on how you respond to constraint).

But how fascinating, when you think of ancient humans painting on the walls of caves, that we can find ways of applying our mark to almost anything! And food for thought too about how easily we pick up another piece of paper, and another, and another. Or a screen. Or a phone. No shortage of welcoming surfaces for us.

Some entrants, defeated by the difficulty of writing on wrappers, 'cheated' by writing (or typing) onto labels and sticking these to the wrapper. Others stuck the whole wrapper to another backing material and wrote on that.

I love all the rebels. That's another thing about constraint: it feeds rebellion. Without something to rebel against, where would any art movement be?

But I haven't mentioned the obvious constraint of handwriting. Is handwriting getting less legible? Possibly. Certainly some excellent WrapperRhyme examples were extremely hard to read, and without the transcript one would have been seriously lost. No spell-check either, so some spelling was ... creative.

There were constraints of length in the rules too (but many people forgot about them, either accidentally or on purpose) and constraints of the size of the wrapper in the rules (some huge envelopes dropping through the letter box showed what many poets thought about THAT).

And there was the constraint of having to mention the product (or some aspect of it) somewhere or somehow in the content of the poem.

For some writers this was a key advantage because it gave them something to play with. Others wrote whatever they wanted to write anyway and the product just got a mention in a free-floating title (and wrapper-rhymes don't have to have titles at all, though of course they may).

I had expected the rhymers to write on the back of the wrapper, simply because it hadn't occurred to me to do anything else (the Ted Hughes prototype was definitely on the back). But some of them incorporated their rhyme into the actual design on the front of the wrapper. Sometimes this worked rather elegantly. At other times, well ....

Right now we're logging the entries carefully (I'm up to number 88 so far but there is a huge box of them waiting) and beginning to work on making all of them into something else, namely an exhibition/installation. It's going to be really interesting working out how to display a two-sided product in multiple sizes and materials.

But Jenny Elliott and I have a million ideas for handling this constraint. Constraints are great.