This article provides some tips for customizing and testing ZPL labels.
Development
A ZPL label template can be edited with a simple text editor such as Notepad. These ZPL templates are assigned to labels in Report Setup at Core - Setup - Reports. The best practice document, BP0087 ZPL Basics, explains common ZPL codes, provides several examples of label code and the resulting output, describes how ZPLs are measured, and other tips. This will get you started on the way to making customizations. A further reference is the ZPL Programming Guide which you can find online at Zebra's website.
Available System Tags
The LabelTags spreadsheet (attached) lists tags you place into ZPL that can be filled in by FeneVision for you. One example is the !ORDERNO! tag. When you place the !ORDERNO! tag into a ZPL template, FeneVision will place the associated order number into that location when printing. The spreadsheet also notes which tags are available for each of the label types, see the Part & Warranty, Wrapper, NFRC, etc. columns.
Testing
There are methods to view your changes without a physical printer and without wasting labels. The best practice, BP0136 Setting up Generic Text Printer for ZPL, explains how to setup a generic text printer that saves the output of ZPL to a file (or files) that can be viewed with the online program at http://labelary.com/viewer.html.
An alternative to setting up a Generic Text Printer is to use the Microsoft XPS Document Writer. The Microsoft XPS Document Writer is available with Microsoft operating systems, and if you do not see it in your printer list, this feature can be quickly enabled with instructions you will find online. In Core - Setup - Reports, assign the Microsoft XPS Document Writer as the printer for the label you are testing. When you print the label from FeneVision, a few files will be generated with extension .oxps, typically placed in your documents folder. You view these label output files with http://labelary.com/viewer.html. You must copy the output in the files into labelary in the order the files were generated, otherwise you will likely receive an error or garbage from labelary! This rule holds true no matter what method you use for generating the label output files.
For a virtual printer with richer features, you may want to look at https://github.com/porrey/Virtual-ZPL-Printer.
Displaying Images on Labels
Perhaps you want to add your company logo, or some other image, to a ZPL label. The best practice, BP0127 Image to ZPL Code Conversion, explains how to take a digital image and convert it to ZPL code. This process requires the ZebraNet Bridge available from Zebra's website.