"Prefs > Languages > Tcl > Syntax Checking"
I see no such path.
I see "Preferences -> Language Help" or "Preferences -> Syntax and Spell Checking".
When I follow some similar path I see no option to change any individual syntax check option.
"Preferences -> Syntax and Spell Checking -> Language-specific syntax checking properties" only has a check box to turn syntax checking on or off.
I am using Komodo version 10.2.0, Build 89833, platform win32-X86
"I'm not a Tcl developer, but it sounds to me that there is a slight syntactical difference between versions 8.5 and 8.6."
I am not a TCL developer either but I am smart enough to know that Komodo should not be looking for installed TCL in order to determine how to check version specific syntax.
What if TCL is not installed on the system used for Komodo?
You specifically stated there was a difference so I am asking for a pointer to some documentation or some specification that supports your conclusion.
"So upgrading to 8.6 would make Komodo apply the 8.6 ruleset to your syntax."
Upgrading TCL to any version does not have anything to do with Komodo as far as I can see. You yourself indicated that for Komodo "The syntax checker is a proprietary component" so I fail to see the connection to "installed TCL" if I am just opening a TCL file to perform some basic edits or syntax checking.
You are not helping, but rather just raising more questions.