HTML XHTML

Previously, Server-Sent Events (SSE) taught the browser to open EventSource and receive a one-way server text stream — live updates, not document syntax history. This lesson leaves streams behind and closes the HTML course’s optional history track with XHTML: HTML written under XML rules. You may still meet old books, certificates, or snippets labeled XHTML 1.0 / 1.1. Scope stays practical — what was stricter, what HTML5 changed, which habits still help — not XML schemas, application/xhtml+xml MIME battles, or a full polyglot publishing course.

Why XHTML in an HTML course

Beginners hit “XHTML Strict” titles and wonder if they must rewrite every page. They do not — HTML5 is the mainstream teaching and browser target. Still, knowing the old strictness explains why tutorials demand lowercase tags, quoted attributes, and <br />. After SSE’s “server pushes events,” this lesson’s split is different: markup rules and history, not realtime APIs. You need the idea of XML-flavored HTML, a short habit table, and two tiny contrasts — enough to read legacy material without building an XML toolchain.

Direct answer

1) XHTML = HTML formulated as XML (stricter syntax expectations).
2) Classic habits: lowercase element/attribute names, quoted attribute values, explicit empty elements (<br />, <img … />).
3) Modern default: HTML5 with <!DOCTYPE html> — parsers are more forgiving.
4) Clean markup still matters for accessibility, maintainability, and tooling — HTML5 is not a license for broken trees.
5) For new projects in this course, use HTML5 patterns from earlier lessons.
6) Use this page to translate old XHTML advice into HTML5 practice — not to ship a pure XHTML MIME site unless you already know that path.

Tiny empty-tag contrast

Same meaning, two writing styles. Browsers accept both in typical HTML5 pages; the slash form is the visual clue you are reading XHTML-era material.

Reading the contrast

• <br> and <br /> both mean a line break in everyday HTML5 browsing
• The trailing / was required empty-element syntax in XHTML-style XML writing
• Quotes around src and alt are good HTML5 habit and were required in XHTML
• Lowercase img / br matches both modern convention and classic XHTML rules
• This is not SSE — no EventSource, no stream URL, no onmessage
• Do not switch MIME types just because you typed <br />
• Keep intros tiny: one contrast, one idea

Tiny well-formed mini page

A short document that follows habits both eras respect: doctype, charset, quoted attributes, closed elements. Stay on HTML5 doctype even when markup is tidy.

Reading the mini page

• <!DOCTYPE html> marks HTML5, not an old XHTML doctype
• lang, charset, and quoted attributes are durable good habits
• Every opened non-void element is closed — XML-era discipline that still helps humans and tools
• alt on the image is accessibility, not nostalgia
• Still unrelated to SSE streams or Web Workers
• If an old tutorial shows xmlns and XHTML 1.0 Strict doctype, map the habits here and keep HTML5 for new work
• Next steps in learning are usually CSS/layout courses — not forcing XML MIME on production

Choosing HTML5, XHTML habits, or old tutorials

• New page in this course: HTML5 doctype + clean habits from earlier lessons
• Reading a 2005 “XHTML Strict” book: translate rules → lowercase, quotes, close tags; keep HTML5 doctype
• Seeing <br /> in a snippet: recognize XHTML-era style; it can still appear inside HTML5 files
• Need live server push updates: that was SSE, not XHTML
• Need off-thread local compute: that was Web Workers
• Building XML schemas or application/xhtml+xml products: beyond this intro/compare lesson

Practice — compare, keep HTML5, contrast eras

1. Read the empty-tag contrast; say which form looks XHTML-era.
2. Skim the habit table; note quotes and lowercase.
3. Read the mini page; confirm <!DOCTYPE html> stays HTML5.
4. Write one sentence: SSE streams server events; XHTML is markup history/strictness.
5. Write one sentence: new beginner projects should target HTML5, not “XHTML Strict forever.”
6. (Optional) Take one messy snippet and quote attributes + close tags without changing the doctype away from HTML5.
7. Course note: this closes the HTML quality rewrite queue’s last session topic.

Easy mistakes

• Forcing full XHTML MIME / XML parsing modes without understanding breakage risk
• Treating HTML5’s forgiveness as permission for inaccessible or inconsistent markup
• Mixing random XHTML-era and HTML5 idioms in one team style guide without agreement
• Confusing this history lesson with SSE (no EventSource here)
• Believing every modern site must ship as XHTML 1.1 Strict
• Copying an old XHTML doctype into a new project “for quality”
• Thinking quoted attributes are “only for XHTML” (they remain a strong HTML5 habit)

Summary

• XHTML was HTML under stricter XML-style rules
• HTML5 with <!DOCTYPE html> is the modern default in this course
• Lowercase, quotes, and clear empty/closed tags still help
• Translate old XHTML tutorials; do not treat them as the only legal future
• SSE was live server push; this lesson is markup history
• HTML rewrite queue for this course ends here — next learning track is typically CSS when that course is published