Labour's supermarket tax proposal?

I can't resist a bit of reading from time to time and so I've eventually drifted to Labour's "Manifesto for Growth".  Even with Labour's recent record on economic matters I thought it would be interesting.  It's not all that interesting (actually pretty boring) but there is one wee thing; this paragraph:

We will work to ensure that Scotland is competitive and will do so through the taxation system, by investing in our transport and communication infrastructure and in skills, so our young people are job-ready and meet the needs of business. 

Elsewhere in the document there are commitments to continue the SNP's Small Business Bonus, to not raise the "tartan tax" and to maintain parity with the English poundage on non-domestic rates (which would actually be a slight rise in business rates, but I'm sure that they didn't mean that or they wouldn't have said 'maintain', they're just unaware of the financial landscape) and Gray recently gave in and accepted that the SNP's Council Tax freeze is the right thing to do.

So here's the question - from which part of the taxation system does Labour intend to find the resources to fund this investment?  They've ruled out most of it and it appears to me that there is one avenue left open by this document.  Remember the Tesco Tax?  The large retailer levy was condemned by Labour when John Swinney proposed it, but so was the Council Tax freeze, free prescriptions, and anything else proposed by the SNP and Labour has performed one volte-face after another.

Yup, I think Labour's proposing a Tesco tax.  Whodathunkit?