Alternatively you can use git tools (command line, app, choose your favourite) to clone the repository locally and switch to the branch of interest, then open up the html file in your browser.
If you want to make a pull request, create a new branch from your preferred starting point (usually gh-pages), naming it something relevant, edit the XML source, build the HTML using ant according to the README instructions, check it looks okay, edit as
needed, commit changes, push them to the repository ("sync" if you're using the github app) then make the pull request from your branch into the destination branch (usually gh-pages).
I say "usually gh-pages" since you can alternatively propose a change to another branch using the same method. If there's a pull request from that other branch into gh-pages, then merging your pull request will update the PR into gh-pages too.
Here's an example to illustrate that last paragraph of gibberish:
A) Xavier creates a Pull Request from branch "my-great-contribution" to gh-pages.
B) You review it and think you can improve it, but it's a slightly complicated improvement that could use separate review.
C) Rather than committing directly to "my-great-contribution" you create a "super-improvement" branch from the "my-great-contribution" branch.
D) You make your changes, commit them and push them.
E) You create a pull request from "super-improvement" branch to "my-great-contribution".
F) Everyone loves your work and your pull request gets merged into "my-great-contribution".
G) Now the state of the Pull Request from "my-great-contribution" into gh-pages is updated to include your improvement.
H) The Pull Request from "my-great-contribution" is merged and now gh-pages includes both Xavier's great contribution and your super improvement.
Incidentally, as long as the Pull Requests are made without squashing the commits all of the change history is retained from Xavier's work and your work.
By the way please don't name your branches this way! Something that reflects the actual content of the change is more helpful, and you can include the issue number. Plus in the PR description if you include words like "fixes #1234" then when the PR is
merged into the gh-pages branch the issue will automatically be closed.
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