Currently I have got this working, it is probably not complete.
Replace the line:
<!DOCTYPE muclient>
in your world file with this:
<!DOCTYPE muclient [
<!ELEMENT muclient
(world|
plugin|
triggers|
aliases|
include|
printing|
timers|
macros|
variables|
colours|
keypad|
comment|
script)*>
<!ELEMENT world (#PCDATA) >
<!ELEMENT triggers (trigger)* >
<!ELEMENT aliases (alias)* >
<!ELEMENT timers (timer)* >
<!ELEMENT macros (macro)* >
<!ELEMENT variables (variable)* >
<!ELEMENT colours (ansi|custom)* >
<!ELEMENT keypad (key)* >
<!ELEMENT printing (ansi)* >
<!ELEMENT plugin EMPTY >
<!ELEMENT include EMPTY >
<!ELEMENT script (#PCDATA) >
<!ELEMENT comment (#PCDATA) >
<!ELEMENT trigger (send)?>
<!ELEMENT alias (send)?>
<!ELEMENT macro (send)?>
<!ELEMENT timer (send)?>
<!ELEMENT send (#PCDATA) >
<!ELEMENT ansi (normal|bold)* >
<!ELEMENT normal (colour|style)* >
<!ELEMENT bold (colour|style)* >
<!ELEMENT colour EMPTY >
<!ELEMENT custom (colour)* >
<!ELEMENT style EMPTY >
<!ELEMENT key (send)? >
<!ATTLIST world
muclient_version CDATA #IMPLIED
world_file_version CDATA #IMPLIED
date_saved CDATA #IMPLIED
auto_log_file_name CDATA #IMPLIED
auto_say_override_prefix CDATA #IMPLIED
auto_say_string CDATA #IMPLIED
beep_sound CDATA #IMPLIED
chat_file_save_directory CDATA #IMPLIED
chat_name CDATA #IMPLIED
chat_message_prefix CDATA #IMPLIED
command_stack_character CDATA #IMPLIED
connect_text CDATA #IMPLIED
filter_aliases CDATA #IMPLIED
filter_timers CDATA #IMPLIED
filter_triggers CDATA #IMPLIED
filter_variables CDATA #IMPLIED
id CDATA #IMPLIED
input_font_name CDATA #IMPLIED
log_file_postamble CDATA #IMPLIED
log_file_preamble CDATA #IMPLIED
log_line_postamble_input CDATA #IMPLIED
log_line_postamble_notes CDATA #IMPLIED
log_line_postamble_output CDATA #IMPLIED
log_line_preamble_input CDATA #IMPLIED
log_line_preamble_notes CDATA #IMPLIED
log_line_preamble_output CDATA #IMPLIED
mapping_failure CDATA #IMPLIED
name CDATA #IMPLIED
new_activity_sound CDATA #IMPLIED
notes CDATA #IMPLIED
on_mxp_close_tag CDATA #IMPLIED
on_mxp_error CDATA #IMPLIED
on_mxp_open_tag CDATA #IMPLIED
on_mxp_set_variable CDATA #IMPLIED
on_mxp_start CDATA #IMPLIED
on_mxp_stop CDATA #IMPLIED
on_world_close CDATA #IMPLIED
on_world_save CDATA #IMPLIED
on_world_connect CDATA #IMPLIED
on_world_disconnect CDATA #IMPLIED
on_world_get_focus CDATA #IMPLIED
on_world_lose_focus CDATA #IMPLIED
on_world_open CDATA #IMPLIED
output_font_name CDATA #IMPLIED
password CDATA #IMPLIED
paste_line_postamble CDATA #IMPLIED
paste_line_preamble CDATA #IMPLIED
paste_postamble CDATA #IMPLIED
paste_preamble CDATA #IMPLIED
player CDATA #IMPLIED
proxy_password CDATA #IMPLIED
proxy_server CDATA #IMPLIED
proxy_username CDATA #IMPLIED
recall_line_preamble CDATA #IMPLIED
script_editor CDATA #IMPLIED
script_filename CDATA #IMPLIED
script_language CDATA #IMPLIED
script_prefix CDATA #IMPLIED
send_to_world_file_postamble CDATA #IMPLIED
send_to_world_file_preamble CDATA #IMPLIED
send_to_world_line_postamble CDATA #IMPLIED
send_to_world_line_preamble CDATA #IMPLIED
site CDATA #IMPLIED
spam_message CDATA #IMPLIED
speed_walk_filler CDATA #IMPLIED
speed_walk_prefix CDATA #IMPLIED
tab_completion_defaults CDATA #IMPLIED
terminal_identification CDATA #IMPLIED
accept_chat_connections (y|n) "n"
alternative_inverse (y|n) "n"
alt_arrow_recalls_partial (y|n) "n"
always_record_command_history (y|n) "n"
arrows_change_history (y|n) "y"
arrow_keys_wrap (y|n) "n"
arrow_recalls_partial (y|n) "n"
autosay_exclude_macros (y|n) "n"
autosay_exclude_non_alpha (y|n) "n"
auto_allow_files (y|n) "n"
auto_allow_snooping (y|n) "n"
auto_copy_to_clipboard_in_html (y|n) "n"
auto_pause (y|n) "y"
auto_repeat (y|n) "n"
auto_wrap_window_width (y|n) "n"
carriage_return_clears_line (y|n) "n"
chat_foreground_colour CDATA "255"
chat_background_colour CDATA "0"
chat_max_lines_per_message CDATA "0"
chat_max_bytes_per_message CDATA "0"
chat_port CDATA "4050"
confirm_before_replacing_typing (y|n) "y"
confirm_on_paste (y|n) "y"
confirm_on_send (y|n) "y"
connect_method CDATA "0"
copy_selection_to_clipboard (y|n) "n"
convert_ga_to_newline (y|n) "n"
ctrl_n_goes_to_next_command (y|n) "n"
ctrl_p_goes_to_previous_command (y|n) "n"
ctrl_z_goes_to_end_of_buffer (y|n) "n"
custom_16_is_default_colour (y|n) "n"
detect_pueblo (y|n) "y"
disable_compression (y|n) "n"
display_my_input (y|n) "n"
double_click_inserts (y|n) "n"
double_click_sends (y|n) "n"
echo_colour CDATA "0"
echo_hyperlink_in_output_window (y|n) "y"
edit_script_with_notepad (y|n) "y"
enable_aliases (y|n) "y"
enable_auto_say (y|n) "n"
enable_beeps (y|n) "y"
enable_command_stack (y|n) "n"
enable_scripts (y|n) "y"
enable_spam_prevention (y|n) "n"
enable_speed_walk (y|n) "n"
enable_timers (y|n) "y"
enable_triggers (y|n) "y"
enable_trigger_sounds (y|n) "y"
escape_deletes_input (y|n) "n"
flash_taskbar_icon (y|n) "n"
history_lines CDATA "1000"
hyperlink_adds_to_command_history (y|n) "y"
hyperlink_colour CDATA "16744448"
ignore_chat_colours (y|n) "n"
ignore_mxp_colour_changes (y|n) "n"
indent_paras (y|n) "n"
input_background_colour CDATA "16777215"
input_font_height CDATA "12"
input_font_italic (y|n) "n"
input_font_weight CDATA "0"
input_font_charset CDATA "1"
input_text_colour CDATA "0"
keep_commands_on_same_line (y|n) "n"
keypad_enable (y|n) "y"
line_information (y|n) "y"
line_spacing CDATA "0"
log_html (y|n) "n"
log_input (y|n) "n"
log_in_colour (y|n) "n"
log_notes (y|n) "n"
log_output (y|n) "y"
log_raw (y|n) "n"
lower_case_tab_completion (y|n) "n"
map_failure_regexp (y|n) "n"
max_output_lines CDATA "5000"
mud_can_change_link_colour (y|n) "y"
mud_can_remove_underline (y|n) "n"
mud_can_change_options (y|n) "y"
mxp_debug_level CDATA "0"
naws (y|n) "n"
note_text_colour CDATA "4"
no_echo_off (y|n) "n"
output_font_height CDATA "12"
output_font_weight CDATA "0"
output_font_charset CDATA "1"
password_base64 (y|n) "n"
paste_commented_softcode (y|n) "n"
paste_delay CDATA "0"
paste_delay_per_lines CDATA "1"
paste_echo (y|n) "n"
pixel_offset CDATA "1"
port CDATA "4000"
proxy_password_base64 (y|n) "n"
proxy_port CDATA "1080"
proxy_type CDATA "0"
re_evaluate_auto_say (y|n) "n"
save_deleted_command (y|n) "n"
save_world_automatically (y|n) "n"
script_reload_option CDATA "0"
script_errors_to_output_window (y|n) "n"
send_echo (y|n) "n"
send_file_commented_softcode (y|n) "n"
send_file_delay CDATA "0"
send_file_delay_per_lines CDATA "1"
send_mxp_afk_response (y|n) "y"
show_bold (y|n) "n"
show_connect_disconnect (y|n) "y"
show_italic (y|n) "y"
show_underline (y|n) "y"
spam_line_count CDATA "20"
speed_walk_delay CDATA "0"
spell_check_on_send (y|n) "n"
start_paused (y|n) "n"
tab_completion_lines CDATA "200"
tab_completion_space (y|n) "n"
translate_backslash_sequences (y|n) "n"
translate_german (y|n) "n"
underline_hyperlinks (y|n) "y"
unpause_on_send (y|n) "y"
use_custom_link_colour (y|n) "y"
use_default_aliases (y|n) "n"
use_default_colours (y|n) "n"
use_default_input_font (y|n) "n"
use_default_macros (y|n) "n"
use_default_output_font (y|n) "n"
use_default_timers (y|n) "n"
use_default_triggers (y|n) "n"
use_mxp CDATA "0"
utf_8 (y|n) "n"
validate_incoming_chat_calls (y|n) "n"
warn_if_scripting_inactive (y|n) "y"
wrap (y|n) "y"
wrap_column CDATA "80"
write_world_name_to_log (y|n) "y"
>
<!ATTLIST triggers
muclient_version CDATA #IMPLIED
world_file_version CDATA #IMPLIED
date_saved CDATA #IMPLIED
>
<!ATTLIST trigger
back_colour CDATA "0"
bold (y|n) "n"
clipboard_arg CDATA "0"
colour_change_type CDATA "0"
custom_colour CDATA "0"
enabled (y|n) "n"
expand_variables (y|n) "n"
group CDATA #IMPLIED
ignore_case (y|n) "n"
italic (y|n) "n"
keep_evaluating (y|n) "n"
lines_to_match CDATA "0"
lowercase_wildcard (y|n) "n"
make_bold (y|n) "n"
make_italic (y|n) "n"
make_underline (y|n) "n"
match CDATA #REQUIRED
match_back_colour (y|n) "n"
match_bold (y|n) "n"
match_inverse (y|n) "n"
match_italic (y|n) "n"
match_text_colour (y|n) "n"
match_underline (y|n) "n"
multi_line (y|n) "n"
name CDATA #IMPLIED
omit_from_log (y|n) "n"
omit_from_output (y|n) "n"
one_shot (y|n) "n"
other_back_colour CDATA "0"
other_text_colour CDATA "0"
regexp (y|n) "n"
repeat (y|n) "n"
script CDATA ""
send_to CDATA "0"
sequence CDATA "100"
sound CDATA ""
sound_if_inactive (y|n) "n"
text_colour CDATA "0"
user CDATA "0"
variable CDATA ""
>
<!ATTLIST aliases
muclient_version CDATA #IMPLIED
world_file_version CDATA #IMPLIED
date_saved CDATA #IMPLIED
>
<!ATTLIST alias
name CDATA #IMPLIED
script CDATA ""
match CDATA #IMPLIED
enabled (y|n) "n"
echo_alias (y|n) "n"
expand_variables (y|n) "n"
group CDATA #IMPLIED
variable CDATA ""
omit_from_command_history (y|n) "n"
omit_from_log (y|n) "n"
regexp (y|n) "n"
send_to CDATA "0"
omit_from_output (y|n) "n"
menu (y|n) "n"
ignore_case (y|n) "n"
keep_evaluating (y|n) "n"
sequence CDATA "100"
temporary (y|n) "n"
user CDATA "0"
>
<!ATTLIST timers
muclient_version CDATA #IMPLIED
world_file_version CDATA #IMPLIED
date_saved CDATA #IMPLIED
>
<!ATTLIST timer
name CDATA #IMPLIED
script CDATA #IMPLIED
enabled (y|n) "n"
hour CDATA "0"
minute CDATA "0"
second CDATA "0"
offset_hour CDATA "0"
offset_minute CDATA "0"
offset_second CDATA "0"
send_to CDATA "0"
temporary (y|n) "n"
user CDATA "0"
at_time (y|n) "n"
group CDATA #IMPLIED
variable CDATA #IMPLIED
one_shot (y|n) "n"
omit_from_output (y|n) "n"
omit_from_log (y|n) "n"
active_closed (y|n) "n"
>
<!ATTLIST macros
muclient_version CDATA #IMPLIED
world_file_version CDATA #IMPLIED
date_saved CDATA #IMPLIED
>
<!ATTLIST macro
name CDATA #REQUIRED
type (replace|send_now|insert) #IMPLIED
>
<!ATTLIST variables
muclient_version CDATA #IMPLIED
world_file_version CDATA #IMPLIED
date_saved CDATA #IMPLIED
>
<!ATTLIST colours
muclient_version CDATA #IMPLIED
world_file_version CDATA #IMPLIED
date_saved CDATA #IMPLIED
>
<!ATTLIST colour
seq CDATA #IMPLIED
rgb CDATA #IMPLIED
name CDATA #IMPLIED
text CDATA #IMPLIED
back CDATA #IMPLIED
>
<!ATTLIST keypad
muclient_version CDATA #IMPLIED
world_file_version CDATA #IMPLIED
date_saved CDATA #IMPLIED
>
<!ATTLIST key
name CDATA #REQUIRED
>
<!ATTLIST printing
muclient_version CDATA #IMPLIED
world_file_version CDATA #IMPLIED
date_saved CDATA #IMPLIED
>
<!ATTLIST style
seq CDATA "1"
bold (y|n) "n"
italic (y|n) "n"
underline (y|n) "n"
>
<!ATTLIST include
name CDATA #REQUIRED
plugin (y|n) "n"
>
] >
However MUSHclient currently objects if you have that in your world file. I will have to investigate this.