Advanced b:match_words Features: Backreferences, Zero-Width Patterns, and Debugging

|\(|escaped parentheses|\)|. These are referred to as back references, or backrefs. For example, > :let b:match_words = '\<b\(o\+\)\>:\(h\)\1\>' means that "bo" pairs with "ho" and "boo" pairs with "hoo" and so on. Note that "\1" does not refer to the "\(h\)" in this example. If you have "\(nested \(parentheses\)\) then "\d" refers to the d-th "\(" and everything up to and including the matching "\)": in "\(nested\(parentheses\)\)", "\1" refers to everything and "\2" refers to "\(parentheses\)". If you use a variable such as |s:notend| or |s:sol| in the previous paragraph then remember to count any "\(" patterns in this variable. You do not have to count groups defined by |\%(\)|. It should be possible to resolve back references from any pattern in the group. For example, > :let b:match_words = '\(foo\)\(bar\):more\1:and\2:end\1\2' would not work because "\2" cannot be determined from "morefoo" and "\1" cannot be determined from "andbar". On the other hand, > :let b:match_words = '\(\(foo\)\(bar\)\):\3\2:end\1' should work (and have the same effect as "foobar:barfoo:endfoobar"), although this has not been thoroughly tested. You can use |zero-width| patterns such as |\@<=| and |\zs|. (The latter has not been thoroughly tested in matchit.vim.) For example, if the keyword "if" must occur at the start of the line, with optional white space, you might use the pattern "\(^\s*\)\@<=if" so that the cursor will end on the "i" instead of at the start of the line. For another example, if HTML had only one tag then one could > :let b:match_words = '<:>,<\@<=tag>:<\@<=/tag>' so that "%" can bounce between matching "<" and ">" pairs or (starting on "tag" or "/tag") between matching tags. Without the |\@<=|, the script would bounce from "tag" to the "<" in "</tag>", and another "%" would not take you back to where you started. DEBUGGING *matchit-debug* *:MatchDebug* If you are having trouble figuring out the appropriate definition of |b:match_words| then you can take advantage of the same information I use when debugging the script. This is especially true if you are not sure whether your patterns or my script are at fault! To make this more convenient, I have made the command :MatchDebug, which defines the variable |b:match_debug| and creates a Matchit menu. This menu makes it convenient to

This section delves into more advanced features for defining `b:match_words`, including how backreferences work with nested parentheses, and provides examples of valid and invalid backreference usage. It explains the use of zero-width patterns like `@<=` and `\zs` to refine cursor positioning during matching. Finally, it introduces the `:MatchDebug` command for debugging `b:match_words` definitions and explains that it defines the variable |b:match_debug| and creates a Matchit menu.