Output "Lorem ipsum" with minimal number of characters
JavaScript (ES7), 326 283 273 249 243 242 chars

_=&gt;""[r='replace'](/./gu,c=&gt;(c.codePointAt()-4**8).toString(32))[r](/\d/g,d=&gt;"  , exum. ".substr(d,2))[r](/^.|\. ./g,x=&gt;x.toUpperCase())


How it works

The first step in my compression technique is to convert the whole string to lowercase (not mandatory, but looks better), and replace each pair of chars in , exum.  (as well as the trailing space by itself) with its index in the string plus 2. This makes the text a valid base-32 number:

lorem9ips69dolor9sit9amet2consectetur9adipiscing3lit2sed9do3iusmod9tempor9incididunt9ut9labore3t9dolore9magna9aliqua8ut3nim9ad9minim9veniam2quis9nostrud94ercitation9ullamco9laboris9nisi9ut9aliquip943a9commodo9consequat8duis9aute9irure9dolor9in9reprehenderit9in9voluptate9velit3sse9cill69dolore3u9fugiat9nulla9pariatur84cepteur9sint9occaecat9cupidatat9non9proident2sunt9in9culpa9qui9officia9deserunt9mollit9anim9id3st9laboru7


The next step is to convert each 4-char run to decimal, then get the character at that code point. This can be done with the following function:

f=s=&gt;s.replace(/..../g,x=&gt;(n=parseInt(x,32),String.fromCharCode(0xD800+(n&gt;&gt;10),0xDC00+(n&amp;0x03FF))))


(Note: Since all digits are 2 or greater, the minimum possible value of four digits is 2222₃₂. This is equal to 95978₁₀, or 176EA₁₆; therefore, code points will never be in the restricted range.)

And now we have our compressed string:




That's 445 chars compressed into 106 chars. The decompression simply reverses this process:


Convert each char to its code-point in base-32, minus 65536.
Replace each digit n with "  , exum. ".substr(n,2).
Convert each letter after a period or at the beginning of the string to uppercase.


The only ES7 feature used is **. Replace 4**8 with 65536 to run in a browser that doesn't yet support ES7.