diff --git a/.github/workflows/linux_tests.yaml b/.github/workflows/linux_tests.yaml
index 89075bbbd..ba8a5fd0e 100644
--- a/.github/workflows/linux_tests.yaml
+++ b/.github/workflows/linux_tests.yaml
@@ -363,9 +363,9 @@ jobs:
           # libtclenvmodules build requirements
           sudo apt-get install -y gcc autoconf
           # manually install tcl9.0
-          curl -L --output tcl9.0b1-src.tar.gz http://downloads.sourceforge.net/tcl/tcl9.0b1-src.tar.gz
-          tar xfz tcl9.0b1-src.tar.gz
-          cd tcl9.0b1/unix
+          curl -L --output tcl9.0b2rc2-src.tar.gz http://downloads.sourceforge.net/tcl/tcl9.0b2rc2-src.tar.gz
+          tar xfz tcl9.0b2rc2-src.tar.gz
+          cd tcl9.0b2/unix
           ./configure
           make -j
           sudo make install
diff --git a/.hunspell.en.dic b/.hunspell.en.dic
index 74403b9a1..541a63756 100644
--- a/.hunspell.en.dic
+++ b/.hunspell.en.dic
@@ -1161,3 +1161,4 @@ Déchard
 getgrouplist
 getgroups
 gcov
+Tcl9
diff --git a/testsuite/modules.50-cmds/440-module-tag.exp b/testsuite/modules.50-cmds/440-module-tag.exp
index 879a093dc..e6f13c0de 100644
--- a/testsuite/modules.50-cmds/440-module-tag.exp
+++ b/testsuite/modules.50-cmds/440-module-tag.exp
@@ -47,7 +47,13 @@ if {[cmpversion $tclsh_version 8.6] == -1} {
     set linenum 14
 }
 set tserr [msg_moderr {No tag specified in argument} {module-tag} $mp/tag/.modulerc $linenum {  } {} {} $custom]
-testouterr_cmd sh {load tag/5.0} $ans $tserr
+# following tests are expected to fail with Tcl 9.0 (as of 9.0b2rc2)
+# see https://core.tcl-lang.org/tcl/tktview/9889f96f4d
+if {[cmpversion $tclsh_version 9.0] >= 0} {
+    testouterr_cmd sh {load tag/5.0} $ans $tserr xfail
+} else {
+    testouterr_cmd sh {load tag/5.0} $ans $tserr
+}
 unsetenv_var TESTSUITE_MODULE_TAG_ERR1
 
 setenv_var TESTSUITE_MODULE_TAG_ERR2 1
@@ -62,7 +68,13 @@ if {[cmpversion $tclsh_version 8.6] == -1} {
     set linenum 17
 }
 set tserr [msg_moderr {No module specified in argument} {module-tag foo} $mp/tag/.modulerc $linenum {  } {} {} $custom]
-testouterr_cmd sh {load tag/5.0} $ans $tserr
+# following tests are expected to fail with Tcl 9.0 (as of 9.0b2rc2)
+# see https://core.tcl-lang.org/tcl/tktview/9889f96f4d
+if {[cmpversion $tclsh_version 9.0] >= 0} {
+    testouterr_cmd sh {load tag/5.0} $ans $tserr xfail
+} else {
+    testouterr_cmd sh {load tag/5.0} $ans $tserr
+}
 unsetenv_var TESTSUITE_MODULE_TAG_ERR2
 
 setenv_var TESTSUITE_MODULE_TAG_ERR3 1
@@ -78,7 +90,13 @@ if {[cmpversion $tclsh_version 8.6] == -1} {
     set linenum 20
 }
 set tserr [string map {<EXTMATCH> (.*)+} [escre [msg_moderr {Invalid option '--foo'} $errmsg $mp/tag/.modulerc $linenum {  } {} {} $custom]]]
-testouterr_cmd_re sh {load tag/5.0} $ans $tserr
+# following tests are expected to fail with Tcl 9.0 (as of 9.0b2rc2)
+# see https://core.tcl-lang.org/tcl/tktview/9889f96f4d
+if {[cmpversion $tclsh_version 9.0] >= 0} {
+    testouterr_cmd_re sh {load tag/5.0} $ans $tserr 0 xfail
+} else {
+    testouterr_cmd_re sh {load tag/5.0} $ans $tserr
+}
 unsetenv_var TESTSUITE_MODULE_TAG_ERR3
 
 setenv_var TESTSUITE_MODULE_TAG_ERR4 1
@@ -94,7 +112,13 @@ if {[cmpversion $tclsh_version 8.6] == -1} {
     set linenum 23
 }
 set tserr [string map {<EXTMATCH> (.*)+} [escre [msg_moderr {Invalid option '--before'} $errmsg $mp/tag/.modulerc $linenum {  } {} {} $custom]]]
-testouterr_cmd_re sh {load tag/5.0} $ans $tserr
+# following tests are expected to fail with Tcl 9.0 (as of 9.0b2rc2)
+# see https://core.tcl-lang.org/tcl/tktview/9889f96f4d
+if {[cmpversion $tclsh_version 9.0] >= 0} {
+    testouterr_cmd_re sh {load tag/5.0} $ans $tserr 0 xfail
+} else {
+    testouterr_cmd_re sh {load tag/5.0} $ans $tserr
+}
 unsetenv_var TESTSUITE_MODULE_TAG_ERR4
 
 setenv_var TESTSUITE_MODULE_TAG_ERR5 1
@@ -110,7 +134,13 @@ if {[cmpversion $tclsh_version 8.6] == -1} {
     set linenum 26
 }
 set tserr [string map {<EXTMATCH> (.*)+} [escre [msg_moderr {Invalid option '--after'} $errmsg $mp/tag/.modulerc $linenum {  } {} {} $custom]]]
-testouterr_cmd_re sh {load tag/5.0} $ans $tserr
+# following tests are expected to fail with Tcl 9.0 (as of 9.0b2rc2)
+# see https://core.tcl-lang.org/tcl/tktview/9889f96f4d
+if {[cmpversion $tclsh_version 9.0] >= 0} {
+    testouterr_cmd_re sh {load tag/5.0} $ans $tserr 0 xfail
+} else {
+    testouterr_cmd_re sh {load tag/5.0} $ans $tserr
+}
 unsetenv_var TESTSUITE_MODULE_TAG_ERR5
 
 # same error rendering than module-tag/module-forbid, so rely on tests made for
@@ -130,7 +160,13 @@ if {[cmpversion $tclsh_version 8.6] == -1} {
     set linenum 29
 }
 set tserr [msg_moderr {'loaded' is a reserved tag name and cannot be set} $errmsg $mp/tag/.modulerc $linenum {  } {} {} $custom]
-testouterr_cmd sh {load tag/5.0} $ans $tserr
+# following tests are expected to fail with Tcl 9.0 (as of 9.0b2rc2)
+# see https://core.tcl-lang.org/tcl/tktview/9889f96f4d
+if {[cmpversion $tclsh_version 9.0] >= 0} {
+    testouterr_cmd sh {load tag/5.0} $ans $tserr xfail
+} else {
+    testouterr_cmd sh {load tag/5.0} $ans $tserr
+}
 unsetenv_var TESTSUITE_MODULE_TAG_ERR6
 
 setenv_var TESTSUITE_MODULE_TAG_ERR7 1
@@ -146,7 +182,13 @@ if {[cmpversion $tclsh_version 8.6] == -1} {
     set linenum 32
 }
 set tserr [msg_moderr {'auto-loaded' is a reserved tag name and cannot be set} $errmsg $mp/tag/.modulerc $linenum {  } {} {} $custom]
-testouterr_cmd sh {load tag/5.0} $ans $tserr
+# following tests are expected to fail with Tcl 9.0 (as of 9.0b2rc2)
+# see https://core.tcl-lang.org/tcl/tktview/9889f96f4d
+if {[cmpversion $tclsh_version 9.0] >= 0} {
+    testouterr_cmd sh {load tag/5.0} $ans $tserr xfail
+} else {
+    testouterr_cmd sh {load tag/5.0} $ans $tserr
+}
 unsetenv_var TESTSUITE_MODULE_TAG_ERR7
 
 setenv_var TESTSUITE_MODULE_TAG_ERR8 1
@@ -162,7 +204,13 @@ if {[cmpversion $tclsh_version 8.6] == -1} {
     set linenum 35
 }
 set tserr [msg_moderr {'forbidden' is a reserved tag name and cannot be set} $errmsg $mp/tag/.modulerc $linenum {  } {} {} $custom]
-testouterr_cmd sh {load tag/5.0} $ans $tserr
+# following tests are expected to fail with Tcl 9.0 (as of 9.0b2rc2)
+# see https://core.tcl-lang.org/tcl/tktview/9889f96f4d
+if {[cmpversion $tclsh_version 9.0] >= 0} {
+    testouterr_cmd sh {load tag/5.0} $ans $tserr xfail
+} else {
+    testouterr_cmd sh {load tag/5.0} $ans $tserr
+}
 unsetenv_var TESTSUITE_MODULE_TAG_ERR8
 
 setenv_var TESTSUITE_MODULE_TAG_ERR9 1
@@ -178,7 +226,13 @@ if {[cmpversion $tclsh_version 8.6] == -1} {
     set linenum 38
 }
 set tserr [msg_moderr {'nearly-forbidden' is a reserved tag name and cannot be set} $errmsg $mp/tag/.modulerc $linenum {  } {} {} $custom]
-testouterr_cmd sh {load tag/5.0} $ans $tserr
+# following tests are expected to fail with Tcl 9.0 (as of 9.0b2rc2)
+# see https://core.tcl-lang.org/tcl/tktview/9889f96f4d
+if {[cmpversion $tclsh_version 9.0] >= 0} {
+    testouterr_cmd sh {load tag/5.0} $ans $tserr xfail
+} else {
+    testouterr_cmd sh {load tag/5.0} $ans $tserr
+}
 unsetenv_var TESTSUITE_MODULE_TAG_ERR9
 
 setenv_var TESTSUITE_MODULE_TAG_ERR10 1
@@ -194,7 +248,13 @@ if {[cmpversion $tclsh_version 8.6] == -1} {
     set linenum 41
 }
 set tserr [msg_moderr {'hidden' is a reserved tag name and cannot be set} $errmsg $mp/tag/.modulerc $linenum {  } {} {} $custom]
-testouterr_cmd sh {load tag/5.0} $ans $tserr
+# following tests are expected to fail with Tcl 9.0 (as of 9.0b2rc2)
+# see https://core.tcl-lang.org/tcl/tktview/9889f96f4d
+if {[cmpversion $tclsh_version 9.0] >= 0} {
+    testouterr_cmd sh {load tag/5.0} $ans $tserr xfail
+} else {
+    testouterr_cmd sh {load tag/5.0} $ans $tserr
+}
 unsetenv_var TESTSUITE_MODULE_TAG_ERR10
 
 setenv_var TESTSUITE_MODULE_TAG_ERR11 1
@@ -210,7 +270,13 @@ if {[cmpversion $tclsh_version 8.6] == -1} {
     set linenum 44
 }
 set tserr [msg_moderr {'hidden-loaded' is a reserved tag name and cannot be set} $errmsg $mp/tag/.modulerc $linenum {  } {} {} $custom]
-testouterr_cmd sh {load tag/5.0} $ans $tserr
+# following tests are expected to fail with Tcl 9.0 (as of 9.0b2rc2)
+# see https://core.tcl-lang.org/tcl/tktview/9889f96f4d
+if {[cmpversion $tclsh_version 9.0] >= 0} {
+    testouterr_cmd sh {load tag/5.0} $ans $tserr xfail
+} else {
+    testouterr_cmd sh {load tag/5.0} $ans $tserr
+}
 unsetenv_var TESTSUITE_MODULE_TAG_ERR11
 
 #