I believe Pega provides the functionality of using XSL using Rule-File-Text and it would behave the same as a normal use case when one XSL is included in other using xsl:include tag, i.e., it would simply replace the instruction with the content of the stylesheet mentioned in the href attribute.
Is that what you have posted in your query? Please correct me if I understood it incorrectly.
Ideally I am invoking PerformXSLT Rue-Utility-Function it takes Rule-File-Text (eg. /webwb/sample.xsl) as parameter . in my scenarion sample.xsl include another xsl file sample1.xsl . while invoking the function , i cud see in the log error , not able to find the sample1.xsl in pega log .
If try with OOTB R-F-T (pal_Graph.xsl) which includes another pal_common.xsl, i still get the same erroe in pega log , not able to find pal_common.xsl .
In my scenario i have created both sample.xsl and sample1.xsl R-F-T in webwb .