Examples of CSS properties practical usage xml, xmlns, etc.

-x-system-font
-xborder-right
XGqw
XHR
XXL
XXX
XXXpadding
XZGA
XZmw
Xbackground
Xbackground-color
Xborder
Xbox-shadow
Xpadding
Xpok
Xposition
Xwidth
x-accordion-toggle
x-article-box
x-btn
x-btn-circle-wrap
x-btn-navbar
x-btn-widgetbar
x-caret
x-cite
x-column
x-comment-time
x-container
x-content-band
x-creative-cta
x-date-mp-next
x-date-mp-prev
x-filter
x-header-column
x-icon-adjust
x-icon-ambulance
x-icon-angle-right
x-icon-arrow-up
x-icon-arrows-h
x-icon-arrows-v
x-icon-backward
x-icon-bar-chart-o
x-icon-bell
x-icon-bell-o
x-icon-bolt
x-icon-bookmark
x-icon-camera
x-icon-chain
x-icon-check
x-icon-chevron-left
x-icon-circle
x-icon-circle-o
x-icon-clipboard
x-icon-cloud
x-icon-cogs
x-icon-comment-o
x-icon-comments
x-icon-comments-o
x-icon-compress
x-icon-credit-card
x-icon-crosshairs
x-icon-envelope
x-icon-eye-slash
x-icon-facebook
x-icon-fast-forward
x-icon-file-text-o
x-icon-flag-o
x-icon-flash
x-icon-flask
x-icon-forward
x-icon-frown-o
x-icon-gamepad
x-icon-gavel
x-icon-gear
x-icon-gears
x-icon-github
x-icon-group
x-icon-hand-o-down
x-icon-hand-o-left
x-icon-hand-o-right
x-icon-hand-o-up
x-icon-hospital-o
x-icon-indent
x-icon-info-circle
x-icon-italic
x-icon-key
x-icon-keyboard-o
x-icon-legal
x-icon-lightbulb-o
x-icon-linkedin
x-icon-magic
x-icon-map-marker
x-icon-medkit
x-icon-meh-o
x-icon-minus
x-icon-minus-circle
x-icon-mobile
x-icon-paste
x-icon-pause
x-icon-phone
x-icon-picture-o
x-icon-plane
x-icon-play
x-icon-plus
x-icon-plus-circle
x-icon-power-off
x-icon-print
x-icon-quote-left
x-icon-rss
x-icon-search-minus
x-icon-share
x-icon-sign-in
x-icon-sitemap
x-icon-smile-o
x-icon-sort-asc
x-icon-sort-down
x-icon-sort-up
x-icon-spinner
x-icon-square
x-icon-square-o
x-icon-star
x-icon-suitcase
x-icon-table
x-icon-tachometer
x-icon-tasks
x-icon-terminal
x-icon-text-width
x-icon-thumb-tack
x-icon-trophy
x-icon-twitter
x-icon-umbrella
x-icon-unlock
x-icon-users
x-icon-video-camera
x-icon-wrench
x-img
x-img-thumbnail
x-input
x-item-frame
x-large
x-main
x-menu-a-text
x-menu-item
x-menu-text
x-nav-tabs
x-nav-tabs-item
x-new-row
x-ph__auth__link
x-ph__button
x-ph__button__fake
x-ph__button__input
x-ph__button_action
x-ph__form__link
x-ph__link
x-ph__link_first
x-ph__link_last
x-ph__menu__button
x-portfolio-filters
x-pricing-column
x-product-box
x-recent-post1
x-recent-post2
x-recent-post3
x-recent-post4
x-recent-posts-img
x-row-fluid
x-scroll-top
x-section
x-share
x-slides
x-sub-menu
x-tab-panel
x-tab-strip-close
x-toc-item
x-tool-close
x-topbar
xalicons
xatyv
xauth-ss-link
xbackground
xbackground-color
xbackground-image
xborder
xborder-bottom
xborder-left
xborder-radius
xborder-right
xborder-top
xbottom
xbox-shadow
xc-item
xcolor
xcssLinkSettings
xdisplay
xdsoft_disabled
xdsoft_label
xdsoft_next
xdsoft_noselect
xdsoft_option
xdsoft_prev
xdsoft_today_button
xecy
xefycan
xemthem
xf-masonry-entry
xf_wylc_page_rele
xfbml
xfilter
xfloat
xfont-family
xfont-size
xfont-weight
xheight
xhfbfile
xhrWrappable
xhtml
xing
xing-icon
xing-link
xing-square
xinwen
xjxfun
xlarg
xlarge
xlarge-centered
xlarge-uncentered
xleft
xline-height
xlink
xls
xmargin
xmargin-bottom
xmargin-left
xmargin-right
xmargin-top
xmas
xmax-width
xmenu
xmin-height
xml
xmlns
xnarrow
xola-custom
xoouserultra-button
xopacity
xoverflow
xoxo
xoxo-danger
xoxo-default
xoxo-group
xoxo-info
xoxo-primary
xoxo-success
xoxo-warning
xp-hamburger__line
xpadding
xpadding-bottom
xpadding-left
xpadding-right
xpadding-top
xpid
xplore
xposition
xpro2
xr_nb0
xr_nb1
xr_pnav
xr_pnava
xr_pnavm
xr_pnavmenu
xr_pnavp
xright
xrotate
xs-hover
xs-margin
xs-padding
xt-archive
xt-megamenu
xtext-align
xtext-decoration
xtext-shadow
xtext-transform
xtop
xtreme-3dbutton
xtreme_button
xunjia
xwhite-space
xwide
xwidth
xwlj
xxlarge
xxlarge-centered
xxlarge-h
xxlarge-uncentered
xxwide
xxxbackground
xxxbackground-color
xxxlarge
xxxx-family
xxxx-style
xyz