itsp/MaxSubscreens is a SAP Parameter attribute which is used to control SAP Gui for HTML, maximum number of subscreens information. This is available within R/3 SAP systems depending on the version and release level.
Below is the standard documentation available and a few details of the attributes values .
Specifies the maximum number of visible screens in the Object Navigator
of the ABAP Workbench.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.